What you do in HS can help, but it's not immediately crucial. You should really focus on a few things:
(1) Have fun. You're a teenager. You don't get those years back.
(2) Do well in school. You don't have to be number 1 in everything, but do some AP classes, get into a nice school, get scholarships to cut down on cost. Find friends who are academically supportive.
(3) Don't get in trouble with the law. You never know when it can bite you.
Take economics. Take wood shop. Take underwater basket weaving. Take the weirdest class available. Just don't take only science courses. It's too early to just narrow your career that much. This is the one time to explore without consequence (unless you don't mind paying for an extra year or two of college when you change your major)
You'll be best served in primary care by developing your interpersonal skills, interests, and experiences throughout high school and college. Primary care requires you to be able to relate to your patients, so go out and become a dynamic person with a wide range of interests and hobbies so that you can better connect with them and develop trusting, meaningful relationships.
Enjoy high school. Take whatever you want that allows you to graduate on time and not feel braindead during your time in class. IF you feel the need to take college courses in high-school (AP or community college course, etc.) i don't recommend trying to transfer any science courses to your undergrad institution. There are 2 reasons: 1) those basic level science courses are usually relatively easy As for people that have a science inclination that you will miss out on because transfer credits don't usually go on your undergrad's transcript as a letter grade. 2) there are some medical schools that don't accept AP credits or community college courses for the core sciences.
Also, I don't recommend BS/MD programs or their equivalents to other professional programs because most HS students have no idea what it is they want to do for the rest of their life. Don't pigeonhole yourself in an educational path you may not want to pursue down the line. Most students who are competitive enough out of HS to get in a BS/MD program out of HS have the fortitude to make it in the normal app cycle if medicine is still their passion when the time comes.