Pilot reported a NMAC during takeoff when an ultralight aircraft crossed directly over them. Reporter stated they saw the ultralight moving across the runway during takeoff roll but elected to continue; realizing too late that the flight paths would cross.

Narrative

I was flying solo in a high-wing LSA (Light Sport Aircraft) undertaking some pattern practice at ZZZ when I had a near miss incident with an ultralight aircraft. Afterward; I recognized I made a series of mistakes which developed into a near miss incident.This was my last landing at ZZZ before returning to my primary airport. I was at approximately 1000 feet on a left downwind for Runway XX and made a radio announcement on the CTAF when I saw an unusual object quite low; moving east across an agricultural field toward Runway XX. Due to how the sunlight was on the object I did not immediately recognize what it was- which first appeared as something like a small white rectangle. After a few moments I realized it was an ultralight aircraft which was making its way toward Runway XX; I did not hear any radio broadcast from the ultralight. Those observations should have been my first warnings of the complications to come. Additionally; that was the first time I had seen an ultralight in flight while I was piloting a small aircraft.The ultralight landed and made a touch and go while I continued in the pattern; turned onto final and announced on CTAF for Runway XX. The ultralight appeared to be well away as I slowed my approached for landing. By then; I lost track of the ultralight and I was landing. I made a full-stop and taxied back to Runway XX. I did not see or hear from the ultralight while I was taxiing. I should have made more of an effort to try and track the ultralight while I was on the ground.I stopped at the hold short line for Runway XX and looked right (north) for other aircraft inbound for Runway XX and glanced left to see the area was clear. I failed to take a thorough look to the left. I made and announcement on the CTAF that I was taking Runway XX for take-off. I turned on to Runway XX; added full power and began my take-off roll; only then did I see the ultralight which appeared to be flying parallel to Runway XX- but I thought it was some distance away from the far end of the runway. Its altitude was approximately 200 to 300 ft. AGL slightly west of the runway.As I accelerated; monitoring the airspeed indicator and maintaining runway alignment I realized the ultralight was actually moving east across my intended take-off flight path. I thought the ultralight would cross my path early but my awareness and understanding of its capability was completely wrong.I should have immediately aborted my take-off. I believe I had enough runway to do so. The ultralight was flying so slowly relative to my take-off speed I flew under its path; I flew level for a short period to try and not get any closer than I already was. I did not note my altitude but estimate I was about 30 to 50 feet AGL when I passed under. I left the airspace and returned to my primary airport without further incident.I have replayed the incident in my mind over and over; to try and account for my errors and outright poor judgment.Up front; time was a factor as I needed to return the aircraft. I did not take a few extra moments to confirm the airspace to the left (south) and around my take-off runway was actually clear of other aircraft. Secondly I lacked good situational awareness of the other factors at play- the ultralight's capability and the other pilot's intent relative to my aircraft's capability. I did not realize just how small and slow ultralights are compared to me operating in a small airplane; nor did I realize how close the ultralight was; when I was on my take-off roll; since it was so small. I did not know pilot intent without a radio broadcast but in retrospect that didn't matter so much. The fact the other pilot was in the airspace should have made me realize at the time (emphasis here) I should not continue and create a problem or make existing problems worse.Up to this flight I had considered myself a safe and conservative pilot. I learned much more than I anticipated on this flight; albeit by the incorrect wayof learning. I will not make these kinds of errors again and plan to be a truly safer pilot for others as well as myself.