If you were (or are) a professor, would one bad grade spoil your opinion of a student?

I started off on the wrong foot this quarter letting some personal issues interfere with my studying (that’ll teach me). So I was already feeling pretty anxious about a midterm in one of my classes today, when my professor came up to me and said that she thought I’d make an excellent candidate for grad school and that I should come speak to her about it sometime. I really, really look up to this professor… but like I said, I wasn’t prepared enough and I think I did awful on the midterm. Now I’m worried what she’ll think of me when that grade comes back.

Should I be worried about this? Do you think one bad exam grade can ruin a teacher’s opinion of a student?