During one of my undergraduate semesters I was pretty depressed (for various personal reasons) and was struggling with completing my coursework. One class in particular didn't have a final exam, there was a just a final essay to turn in worth 25% of the grade. I was really out of it, and in the end I couldn't meet the deadline and didn't even turn it in, I was so unable to concentrate that I was willing to just accept my fate.
For whatever reason, my professor gave me a B- in the class, which is just impossible. Though I did do reasonably well on the rest of the coursework, the highest I could've gotten was 75%, not to mention if there was some bigger penalty that my university had for not attending/doing a final assignment (like getting an incomplete or something, I have no idea). It's unlikely the class was curved that much either...I don't know whether it was a grading entry error, whether the prof accidentally swapped my grade with another person's, or if she just took pity on me (I had mentioned that I was going through some personal issues when I turned in an assignment late during the semester), but for whatever reason I got a B-.
At the time, I was surprised and just accepted it. But as I started to feel better I felt extremely guilty about not turning in the essay, and months later (I've since graduated) I sent my professor an email with the paper attached basically saying "Really sorry I didn't turn it in, I was feeling depressed at the time, I should've turned it in back then, here it is", to which she just hasn't responded. I'm fairly certain she doesn't care at all, but it's been bothering me for a while now.
I'm not sure what to do - should I turn myself in to the school? I feel guilty about the whole thing, but what's worrying me as well is that I also don't want this to bite me in the ass down the line later in life. Can I be punished for not turning the essay, or not telling my professor the grade might have been too high? Was it a mistake to email my professor at all afterwards, maybe I'm causing a problem for her? All in all, I'm really not sure what to think or do.