Couple of things:
1. You're young so you cannot be absolutely certain that you want to be a physician in the future. However, it's an admirable goal. Just remember to keep your options open during college.
2. A 3.3 GPA in HS won't preclude you from getting into med school, residency and being a physician. Yet, I have to make it clear - it will be a tough road. HS is honestly the easiest part of the journey - it allows you to explore and make mistakes w/o dinging your "real" GPA (i.e. your college sGPA and cGPA). You will have to put in close to 100% focus from the jump because the HS to college jump hurts many strong students (e.g. kids who cruised through HS w/ 3.9+).
3. The game plan is simple but the execution is tricky:
- Pick a marketable and interesting major (if you're interested, you'll tend to do better).
- Utilize your institution's learning/tutor center, TA office hrs (or whatever your school calls it), and work w/ friends that are at (or slightly above) your academic competence since this will force you to improve, study smart (don't try to cram - the more you learn, the better you do on exams)
- Keep a 3.7+ sGPA/cGPA. Don't overload w/ tough classes and don't overdo things - take the time to build good study habits and gradually increase the difficulty of your course load (spread your pre-reqs). Due to the way GPA is calculated, your first 2 yrs of courses will hold more weight than the latter 2 (so focus on doing as well as possible in the beginning)
- Don't get involved in too many clubs in the beginning - pick a club or two, sign up for clinical volunteering/shadowing opportunities, and have some fun