I agree with those who say, wait and see, you may get a better grade than you think. This has happened to me enough in 4 semesters that I shouldn't be surprised by it anymore, but I was when it happened again this past semester.
I've got two grades back so far out of five, and I got an A on an essay exam I thought I bombed bad enough for a C, and got a B+ on a multiple choice exam that I thought I nailed, I was 100% confident in all but one answer, and 95% confident in that one.
So, one more time: the exam that was tough for you, was tough for everybody. The exam that was easy for you, was easy for everybody. The curve, accordingly, will reflect this.
Good luck on that exam, btw.