This might make you feel better: I did the same thing. In fact, I made several mistakes.
1) I put in the wrong dates on my application for one of my jobs, which did not match my resume.
2) I misspelled the name of one of my positions on my resume. In fact, it was the job I just held and referred to in my personal statement.
Stupid? Yeah, of course. I stressed over it too, but in the end, just decided to leave it alone. Why pull attention to it? That'll only guarantee that the mistake is found.
Who knows... maybe that was the difference between an acceptance or rejection at Harvard. But what's done is done. Point is, I got into great schools, and the ones who admitted me I expected and the ones who rejected me I expected. Didn't seem to make much of a difference to me.
Good luck. But I do feel your pain.