I think the best thing you can do for yourself is to do what makes you the happiest and even more so what gives you the best chances at excelling. Im senior graduating this June and I been in your boat and I wish someone sat down with me years ago when I was being so indecisive--when I thought being a Bio major was just as important as getting into medical school or when I thought it was the "honorable" thing to do but at the end it does not matter.What matters are your numbers at the end of the day. Don't even doubt yourself, you are better off pulling stellar grades on your social science classes (if thats what you enjoy and do well in) and taking your pre-med preq(plus biochem, genetics, physiology) slowly. Don't rush just take one or two at time....rock them! Do research on the side....Now I can almost guarantee you that if you do that you will beat a lot of bio students who have less then stellar grades to med school. I was bio student and i know how it is. The upper level bio classes are killer, well at least in my school--its hard to pull off A's and this pulls your GPA down.
Also about being prepared for med school...trust me no one major can prepare you or anyone for the rigorous of med school, my bf is doing MD/PHD and he had BioEng background and he even struggled through his first two years of med school, my point is everyone is at equal footing, and med school is not like undergrad...so don't waste your time worrying about that. Just focus on your grades! the preq classes and research and you'll be good to go