i would recommend to not major in a science unless you are truly fascinated by a specific subject. humanities were always much easier for me so i majored in political science which opened up a lot of time for me to party, get high, have sex, read, go to concerts, watch movies, etc. i think you'll be a much more interesting person when all is said and done if you're not in a library for your 4 years of college like so many pre-meds i meet. some people's ambition to get into med school takes up so much of their time, thought and focus, that they end up bored and lonely later in life. don't let that happen to you. either way, handle what you have to handle. get good grades and study at least 3 months UNINTERUPTED (6-8 hours a day) for your MCAT. you will not want to take it twice and i'm convinced its the most important part of your application. others can disagree with that, but its my own conclusion based on knowing lots of people that have gone through this.
furthermore, try and shadow a doctor or work in a hospital WITHIN YOUR FIRST YEAR OR TWO of college to make sure being a doctor is what you want to do. otherwise, taking all those hard classes will have been a complete waste of time. I have NO idea why you want to be a doctor or how you know this early in your life, but to each his own. do NOT glorify the medical profession in your brain on a naive, immature level. it is HARD work. hard work in itself and hard work to even get there in the first place. it is a serious commitment and you must truly be enthralled with medicine and its potential for humanity. once you have decided medicine really is for you, never get discouraged by anybody, stay your course and make sure college is the best time of your life. do ONLY things that interest you or you will hate yourself later because of it.if you don't take my advice, you will only have yourself to blame. i think this is the longest post i have ever written, so i hope it helps you. best of luck.
-mota