A light aircraft pilot reported they flew near terrain attempting to remain VFR in IMC conditions. Reporter received an approach clearance from ATC then cancelled IFR while still in IMC and descended below the MDA.

Narrative

I was PIC of a single-engine; low-wing airplane departing my home non-towered airport (2W5) on a local VFR flight around 1600 local. My intent was 'just a quick pattern session.' Preflight weather showed ceilings in the area generally 500-700 feet AGL with better ceilings to the north. Surface temperature at departure was about 1°C. I recognized this was marginal; but I assumed that in the worst case I could stay below the ceiling in a tight pattern and land.I did not file IFR and I did not set up an IFR 'escape.' The GNS 430W did not have 2W5 or the RNAV (GPS) RWY 2 approach loaded; and my iPad with charts was still in my bag. I also later discovered that my yoke mount only reliably holds the iPad; not my iPhone.On takeoff; I entered cloud or very marginal VMC around 400-500 feet AGL. I began a crosswind turn trying to remain below the ceiling; but as I eased lower I saw trees uncomfortably close and had no reliable horizon. I realized I was on the verge of scud-running over wooded terrain; so I abandoned the idea of staying below the layer; leveled briefly; and then climbed into IMC.I climbed through a thin layer and was on top by roughly 1;000 feet AGL. At that point; I first called 'Requesting priority' on 121.5 with no response; then called on a Potomac Approach frequency I had used recently. Approach answered; acknowledged the emergency; and gave me a heading (initially 190; then right turns to 240 and 260). I selected 2;000 feet MSL and remained at that altitude. While being vectored at 2;000 feet I was task-saturated trying to catch up. I reached back for my iPad; discovered the iPhone would not stay in the mount; entered 2W5 into the 430W; and loaded the RNAV (GPS) RWY 2 approach. I then got the same approach displayed on the iPad. Approach told me to expect the approach from JAAAK and eventually cleared me.After crossing JAAAK I turned correctly toward the next fix (GILBT). However; I had failed to delete the hold-in-lieu-of-procedure-turn at JAAAK in the 430W. As a result; the GPS remained in 'hold' mode and the HSI showed a FROM indication off JAAAK rather than a clean TO leg to GILBT. I used the magenta line as a rough reference while I worked to fix the sequence. During this heads-down work I allowed my altitude to sag from the required 1;800-foot segment altitude to about 1;600 feet. I noticed this; applied full power; and immediately climbed back to 1;800 feet. Terrain was not a factor in this particular area; but it was still an altitude error caused by distraction and poor task management.I then corrected the navigation by activating the proper leg and proceeding inbound via GILBT. Once established; I intercepted and followed the advisory vertical guidance (LNAV+V) and flew the approach at about 90 knots. Lateral and vertical tracking were within one dot. Straight-in MDA for this approach is 600 feet; circling MDA is 700 feet.Near the missed approach point; I finally saw the runway environment essentially below and just ahead of me; but not in time to make a normal; stabilized descent from MDA. I briefly started a steeper descent; then realized I could not safely land from that position. At this decision point; instead of executing the published missed approach and requesting vectors to a nearby airport with better ceilings; I made a poor decision. I canceled IFR with Approach and flew a very low; tight VFR traffic pattern under what I estimate was about a 700-foot ceiling; effectively at or below circling MDA. I used partial flaps; kept 65-70 knots; remained in sight of the runway the entire time; and landed uneventfully. About 20 minutes after I put the airplane away; the ceiling began to lift and the sky started to clear; highlighting how unnecessary the risk had been.In retrospect; the chain of events started with a bad go/no-go decision and overconfidence. I underestimated what 'worse than forecast' could look like; especially with low stratus and near-freezing temperatures. I launched VFR for a non-essential flight without any IFR backup prepared in an environment where inadvertent IMC and icing were very real possibilities. Once airborne; I initially tried to 'stay under' the layer; which could have led to controlled flight into terrain. To my credit; I did recognize that risk and chose to climb; declare an emergency; and work with ATC. However; I then allowed my workload and home-field familiarity to erode altitude discipline on the approach and; most importantly; I chose to cancel IFR and scud around the pattern instead of flying the missed and diverting or holding.Human performance factors included invulnerability ('I'll just stay below it'); impulsivity ('just a quick pattern'); macho ('I can make this work at my home field'); and some anti-authority (substituting my improvised low pattern for a published missed approach and alternate strategy). Cockpit setup and equipment contributed: no preloaded approach; no alternate plan; and no secure mount for my phone increased head-down time when I could least afford it. The unresolved hold at JAAAK in the GPS created a confusing navigation picture that I tried to fix while close to a step-down altitude; leading directly to the brief descent below 1;800 feet.To prevent recurrence; I am revising my personal SOPs and minima. I will no longer depart VFR for 'just pattern work' when ceilings are below about 1;500 feet AGL or visibility below about 5 miles; especially with near-freezing temperatures and low overcast. In such conditions I will either not launch or will only depart on a fully briefed IFR flight with a clearly identified alternate that has higher ceilings and a more favorable approach. For any marginal-weather flight I will have the home approach and at least one alternate preloaded in the panel GPS and on the iPad; with the iPad mounted and powered before engine start. On approaches; segment altitudes and MDA will be treated as hard floors; if the navigation picture is not fully consistent with the plate; I will level or climb until it is. If the runway environment is not in sight in time to allow a normal stabilized descent from MDA; I will execute the published missed approach and work with ATC for either another attempt or a divert. I will not cancel IFR simply to fly a low-altitude VFR pattern under a marginal ceiling again.