There's something I drew once that I still feel really guilty about, and it's something I struggle with moving on from despite feeling like I should.
One time, a couple years ago, I took a commission, and for it I drew characters that were very close to being basically on a cub level, and I wasn't really aware of it at the time, I just looked at the characters' DOB and thought "oh, I can draw them as being like 18+, that's fine", so I did, but after drawing it, I just still felt really guilty about it, and realized later the canon age of the characters, which made me feel pretty awful about the piece, so I just decided to not post it, and told the commissioner they could post it if they kept me anonymous and clarified the characters were meant to be 18+. (it was the main characters of Go, Dog. Go! for context)
I still deeply regret this, and I've tried moving on from it since I know I have not drawn any characters like that since and will not take any characters like that, but no matter what, it still just kind of haunts me. I dunno, just wanted to get this out since it has been gnawing at me for a long while.