I think that the number of science courses and how well you do in them has to do with a few factors: your social life, your study habits, and your school to name a few. I took orgo, bio, orgo lab, bio lab, and stats and got straight Bs all year long. I wish that someone had just told me to take orgo alone, and then double up on physics and bio. But then again, I'm the kind of student that has to really study, and who also very much values her social life. Additionally, four classes a semester is a full class load at my school. Your school may require more per semester. The information you learn in these courses you will need to retain (or re-learn) for the MCATs, so really fully absorbing them is important. If I were you, I'd drop one class and take an easy humanities course if you really want four classes. The next year I took physics, intro to neuroscience, another physics class, and then intro to drawing. It was great, and I got the As I needed to make myself a competitive applicant again.