Plan to major in the field that most interests you, not just the one you do best in. Being premed is common but many or most students discover other interests in college or don't get the grades. To be most competitive for medical school you should be able to handle calculus based physics and a lot of chemistry. To major in physics you will need plenty of math. Eons ago I hated physics, majored in chemistry, liked some biology but the state of that field wasn't as interesting as now (too much classification then, now more chemistry based) and then went to medical school. I know of medical specialties where physics interest is an asset, and others where chemistry is, etc.
You do not have to know your major when you start college. You do need to know the courses required for medical school admissions so you can most efficiently plan both premed and major courses. The biology courses are the least of your worries for medical school purposes (remember that they expect to teach you the material needed in medical school, they want you to have the math/physics/chemistry, not the anatomy and physiology, etc). Calculus plus chemistry first semester plus other courses to meet breadth reqs. Physics when you have enough math. Try to take the toughest courses and as many credits (ie not an easy load) to best prepare you for working hard and to present the best transcript when competing for a spot in a medical school, as well as to stretch yourself and learn the most. Doing the minimum won't be sufficient. I'm sure every college has suggested courses and when to take them available through their premed info.
As a chemistry major I found a lot of physics in physical chemistry- enjoyed the QM, not the thermodynamics. I waited to take an honors biology sequence that required organic chemistry- be sure to check the options available to you at your particular college when deciding which biology courses to take, both for a major and for medical school. Try to be in an honors program to get the most out of your classes, also.