Professor gave me a higher grade than I deserved. What should I do?

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.

Don't worry about it. No one's going to come after you for failing to turn in an b.com/tag/essay">essay in some random course. No one's ever going to b.com/tag/check">check and, if they did, they probably won't care too much.

Should you turn yourself in? No. There's absolutely no reason to turn yourself in. You've done nothing wrong. The professor is the one responsible for assigning your b.com/tag/grade">grade correctly. For all you (or we) know, they felt you deserved a B-.

Should you have emailed your professor the b.com/tag/essay">essay? Probably not, but mostly because they probably don't care. I doubt they read it and I very much doubt that you caused any problems for them.