Should I withdraw from my Genetics Course?

I am a post bac student taking my sciences to get into med school at stony brook university. For the summer I decided to take a genetics course... unfortunately I am not doing so well... I have about a C- but maybe even lower because I didn't do so well on my last exam. I was thinking about withdrawing... but I've never done that before. Will this withdrawal from genetics ruin my chances of getting into med school? I have until August 14th to decide. Any advice would be greatly appreciated.