Hello Armaan -
At this point, I would recommend working on your grades in school and your extracurricular activities. You can start looking into options for undergraduate colleges and determine what you can do now (and in High School) that will help you get into a good undergraduate program. A lot of better 4-year universities will be looking for good grades in more difficult courses (International Baccalaureate and Advanced Placement) in addition to outside activities (sports, music, art, etc.). Find something that interests you and start doing it.
More specifically for the medical field, the University of Manitoba's Medical School offers a lot of support and resources for High School students through their website (http://umanitoba.ca/faculties/health_sciences/medicine/admissions/8822.html) under the "information for high school students" section. This could be an exciting opportunity to get involved in right when you enter high school so you have a full 4-years to determine if you even want to do sports medicine. It can also help you build your professional network while still in High School, which can come in handy when you need letters of recommendation and shadowing experience to get into undergraduate school as well as medical school.
Finally, once you enter college, make sure you study! Your grades and exam scores can make or break your application to medical school and it is important not to become overwhelmed by the independence and allow your grades to slip. Once you feel comfortable with your studies, look for local clubs or groups on campus for future medical professionals to further expand your professional network and provide opportunities to further expand your resume for medical school.