The image was 800x600, but I don't believe it was actually paint.net's fault anymore, as my laptop seems to be having weird triangular artifacts on any app (even with chrome being the only thing open)
Posted this wacky image on Reddit to r/softwaregore because I thought it was funny how paint would let me draw (not very well) outside the box. Developer said I could fix it by toggling hardware acceleration. Didnt really seem to work. GPU was a GTX 1060 6gb (mobile) and i did not have this bug on my 2 year old (4gb)