Well...
I studied behavioral pharmacology and neuroscience as an undergraduate, and found the program to be quite demanding on its own (my college didn't offer minors but most of my electives were music courses).
In addition to your classes, you may wish to distinguish yourself by developing professional relationships with faculty, working as a research assistant, pursuing fellowships, securing internships, attending conferences, completing an honor's thesis, etc.
Don't be too discouraged though: I have a friend who is well on her way to becoming a respected chemist - she is doing her Ph.D at Rochester - but is also a very good soprano (singer). She always took private voice lessons, performed every year in chorus, and took as many music classes for electives as possible. In her limited spare time she continues to take classes (at Eastman) and perform publicly when possible.
In any case, may you find friends and colleagues who are supportive of your serious devotion to multiple vocations - a difficult task in this age of the specialist.