Part 107 UAS pilot reported briefly flying above 400 feet AGL without authorization.

Narrative

I was operating my UAS on a mapping mission with a base station for RTK (Real-Time Kinematic Positioning) corrections. I was running an automated mapping mission using the KMZ file using the app. This was my first operation of the KMZ file as opposed to a KML file. As per the KMZ file; I was having the mission fly to remain no more than 400 feet AGL to the terrain; and in order to maintain a visual line of sight I would move throughout the hilled/undeveloped area in order to maintain VLOS. I would have to remove the cap on the application in order to allow the drone to fly the 400 feet AGL over the hilled areas. This mission became lengthy as I would return to the home start point; move a few hundred feet to a good vantage point that would keep a VLOS; then start the drone and move with it. I would then have to return the drone to home and I came along with it; which proved to be fatiguing. Part of this fatigue was caused by me being hypervigilant to the nearby airport; as there were airplanes practicing landings/touch and gos; (across the highway; but still closeby) and I wanted to ensure no airplanes were moving towards the south (towards me). Towards the end of the mission; the drone began the return to home. During this the drone began to rise to 1000 ft. I was keeping visual line of sight directly and realized it was becoming increasingly difficult to see. I looked at the remote and realized it was at 1000 ft AGL. I then ceased the operation; and took manual control and brought the drone down as quickly as possible. Upon investigating the issue; I soon realized that because I set the return to home safely at 1000 feet; the drone automatically went to that height. My error was not setting it at the 400 feet that I normally set it to. I set the max altitude in the application to 1000 feet; in order to move along the hillsides. (this height would only happen in relation to the altitude). This was also my first operation in a hilled/varying terrain area which added another layer of difficulty. I mostly run mapping missions on smaller flatter terrain. For future flights with varying terrain areas; I will set the return to home altitude no more than 250 feet; which is one of the highest points in the area above my start point. I will also manually fly the drone home at a much lower altitude instead of letting the drone automate itself for a return to home when it comes to unfamiliar sites or varying terrain sites.