You are very naive, but I presume you’re still in high school. If you do earn a Bachelor’s degree and then go to med school and earn an M.D. (medical doctor) degree, NO ONE is going to care whether or not you have a Master’s degree. There IS no higher degree in the professional field of medicine. Oh, you can pick a specialty such as surgery or remain in school and study post doctorate subjects which will enhance your credentials and give you lots of paper to hang on your office wall, but you’ll be kept busy just keeping up with the constant changes in the medical field. Lots of luck!