Gather 'round the campfire kiddies, this will def. make you feel better.
I had a great OChem I prof, and did really well. Second semester, new professor and very different exams. After the first exam, he put a p.p slide of the grade distributions. Highest was an 86 all the way down to a 46. There were a bunch of high 50's, but the only one below those was the lonley 46. I sat in the back, laughing with my friends about the poor soul with the 46. Two minutes later, he hands the exams back. I'm sure you have figured out where this is going, but in case you haven't...the 46 was mine.
Thinking about it now, I should have dropped the class (it would have been my only Withdraw), but I worked my tail off after that only to come out with a C. This story came up in both of my interviews and I used it to talk about how learning to overcome / dealing with failure will ultimatly make me a better med student.
My advice would be if you think you can get a B or better with curves / tudors etc., stick it out. If not, I have heard that one W on the transcript won't kill you. Hope this made someone feel better.