You need to have completed the following courses before taking the MCAT, which is most likely not going to be completed until the end of the Junior year:
Physics 1 & 2
Biology 1 & 2
Gen. Chem. 1 & 2
O. Chem. 1 & 2
Genetics
1 other Biology (Preferaby Physiology)
---> Those that have not taken these courses will likely do much more poorly on the MCAT. That score will always be there when you submit other scores to the school.