I'm not sure if you have your degree yet or not; however, if you do or if you're not far from it, stick with the nursing! Medical schools
look for diversity - not just in skin color, but in educational backgrounds. All things equal, they would quite possibly choose a student with a music background than a science background (assuming that student had the basic requirements for acceptance into medical school). Case in point, my father's best friend is an MD who has a BA in music! So, go for it, if that's what you truly want to be. Remember, medical school is tough, tough, tough, but it doesn't end there... At least three years of residency await you after graduation where you'll most likely work 100+ hour weeks (not months, WEEKS!) at "minimal" pay.
Good luck and let us know what you decide!!!