Science GPA is an incorrect statement for medical school. It is BCPM or Biology, Chemistry, Physics and Math. So if you took an astronomy class or a comp sci class, they will not count in the BCPM GPA (But still will count toward overall of course). However, every biology, chemistry, physics and math course you take will count. Whether it is an english major who only takes the bare minimum or a biochemistry major with all the advanced electives. You are better of majoring in what you like (this may or may not be the traditional bio/chem majors) and taking what BCPM classes you need and any others that interest you.
For example, I was a double major political science/history, with a law degree. I took the basic requirements plus genetics, biochemistry and pathophysiology.
Good luck!