You're in a tough situation. Formal postbacs will often admit you if you've taken Gen Chem, but not if you've taken a semester each of physics and bio as well; they would consider that too many of the prereqs. Thus, you can eaither finish up with your major and do the informal route, taking only the classes you need, or (my recommendation) you can (if you have time) finish the prereqs for med school now, then take a year off to work/study for the MCAT/apply, if you'd like. Also, SMPs are generally for people who want to improve their GPA and get some more experiences in the advanced sciences. Since your GPA is fine, I don't see why you'd want to go there, nor do I think they'd accept you. Good luck to you.