What do you mean by a "Pre-Physician"? You are correct that PA schools generally have similar prerequisites for admissions as most med schools (although PA schools generally require a gross anatomy course if I remember right), and could serve as a potential "back-up plan". However, I believe you need to get an undergrad degree before entering into a PA school as well, so it's generally not a PA -> MD/DO pathway.
However. The road ahead of you is still very long, and you still have a couple of years before you need to settle on picking a major for undergrad. Getting into college is still on your "to-do" list, and you should mostly focus on that! You've still got plenty of time before the nitty-gritty decisions need to come about. But realistically, there is no major that is required to go to medical school, just prerequisite courses. These can be added onto just about *any* major at most colleges (as electives) and will prepare you adequately for the MCAT and fulfilling your prerequisites. So, you can really pick whatever major you want. They don't care what you do, as long as you do it well (i.e. get good grades).
Keep shooting for medical school though! It's much too early to be concerned about back-ups, you have no idea how college will go for you yet, and that's the big deciding factor. You're also five years away from taking the MCAT, which is the major hurdle to determine how "competitive" you are for getting into medical school.
Tl;dr: You can pick whatever major you want. Focus on getting into college in the meantime. You've got plenty of time ahead of you!