i am a new M1 so i may be talking out my you-know-what:
i was a non-science major and had no trouble on the MCAT, though i did take the kaplan class to fill in the holes...
i'm really glad that i got to do something else, and i think it may have made me a better applicant.
but it does make things difficult in the first few weeks of classes. don't go crazy over this b/c i've heard it all evens out, but if you have the time i would really recommend taking cell bio and genetics, maybe biochem... that way you'll have a good foundation for the stuff you'll be learning and won't have to play catchup so much.
that being said, in two weeks of med school you learn about what you learn by midterm in a normal semester, so it'll only help you for a month or so - i still think it would have been helpful and made the transition easier...