You are so young you have an excellent opportunity to get the best background before you get to college. The best things you can take in high school are biological sciences. Biology, Anatomy and physiology if it's offered at your school, organic chemistry if you are ambitious. Advanced math is not needed for nursing, but a little simple Algebra will get you all the math you need for nursing.
Also languages really help, such as Spanish or French, as so many medical terms are Latin based. My knowledge of a second language made medical terminology a breeze for me compared to many of my fellow students.
The great thing about all those courses is that they are great basic courses that look good on your transcipt even if you change your mind later about which path to take.