Don't do it. Seriously. The biggest factor to getting into med school is a high GPA and a high MCAT score. Your GPA needs to be above 3.75, and the higher the better. You can't do anything that might jeopardize this. Ochem is one of the hardest classes pre-meds face, so don't start until you are prepared as possible. I would say that if you've never taken a bio or chem course, take intro bio or intro chem as long as chem 1 or bio 1 are full. I'm tutoring an undergrad right now, and he also has no background in science. He's a smart kid, but he has struggled to pass his science classes, much less get an A. I always thought the best thing for him would have been to go back and take the intro classes meant for someone without high school experience. If you want to do med school, take the slow and steady route so you can get the best grades possible.