Getting into medical schools seems to be a shared goal among many students out there. One criteria for getting into medical school is usually having a minimum math and science g.p.a. of 3.0. Reaching this minimum, however should not be your goal. You should try striving for a 3.6.
A lot of pre-med students start freaking out if they get a C in biology or chemistry or calculus. The fact is you can even fail a science course and still end up with a good math science g.p.a. The problem is that any F's you get, even if you repeat the course are still put into the g.p.a. calculation for your math science g.p.a. (this is aside from your overall g.p.a. which will most likely not calculate any courses you have repeated.)
If you got off to a bad start, then you are best off minoring in a science or math. Hopefully you are good at something enough to pull off A's in all it's courses.
Before registering for ANY math or science class it's very important to chose the time and professor wisely. This can seriously be the reason you get a C instead of a B+. Make sure you visit ratemyprofessor.com to check out if the professor is a toughy or not. If you're not a morning person Don't take a class at 8 in the morn... If you're not used to waking up this early your attention span will not be at it's greatest.
Before registering for a class, see if you can check out the syllabus online first. Try to find out how the course is graded. If writing essays is your weakness you're probably better off avoiding any classes whose papers are a main source of the final grade.
Know your limits and your capabilities. If you calculate that if you get an A for every course in your minor in order to get your math and science g.p.a. high enough, leave room for any B+'s you might get. Crap happens and you might fall a bit in any given course.
With all these in mind you should have a great science/math grade point average. I wish you the best!