update-- that exam that i retook-- i ended up getting 24% higher, this time around!
moral of the story: if you have the option to retake an exam in college or let it go, RETAKE it--especially if it's worth a whole lot and you think you can do better the second time around.
it's tempting to just let it go and be done with it, but one extra night of studying can raise your final grade an entire half letter grade.