OP - The first year of ROTC with or without a scholarship incurs no obligation. If being a military officer is a close second to being a doctor in your career interests right now (as a HS Sr) go ahead and do the first year of ROTC. A large percent of students going to college thinking medicine is their future change their mind. Go to a college you can afford without an ROTC scholarship - you might love the school but not ROTC.
Assess your career interests, GPA, and time constraints of ECs (shadow a Dr. and volunteer in a medical setting) again after the first semester or 3/4 of your first year of college. At that point you will have a better idea how you like Chemistry, Biology, and whatever other premed courses you take. If medicine is still your passion drop ROTC and continue the marathon to medicine. If you change your mind about medicine and have no interest in serving as an officer in the military drop ROTC.
ROTC, even first year, can be a time sink and if you can't manage your time well don't do it even if you plan to drop it after first year. The service obligation of ROTC and HPSP (if you took that too) is very long for an 18 year old to commit to.