If I can give you any advice, it would be to BE YOURSELF! Pick a major that interests you. Get involved in activities that you want to do. Don't become the pre-med clone or think there is a "right" major or activity that you need to do. Please remember that the purpose of college is not to get into medical school, it's to gain a well-rounded education and broaden your mind. Take the classes that interest you and maintain your identity. There are so many people (myself included sometimes) that lose their identities in this process because they try to become what they think Adcoms want them to be. Certainly you need to be involved in extra-curricular activities, but seek out those that really interest you and enjoy this time. Good luck!
Pick the major that will give you the best GPA while allowing you to take the pre-requisite and "recommended" courses. In some schools, biochemistry classes and/or upper-division bio/chem/physics classes are major-restricted. It is best to discuss EVERYTHING with a counselor / pre-medical advisor before signing up for majors and classes.
You will get the highest GPA in a major that you like. You will get the highest GPA in a major that supports your studying habits (if you hate essays and reading, don't go for English majors. If you hate people, don't go for psych/history majors. If you hate math, don't go for math/chemistry majors. If you hate labs, don't go for bio/chem majors).
Just to reiterate, major in something that you like/find interesting that you will get the best grades in and make sure to complete the standard prerequisites as well.
It really doesn't matter, you can major in dance if you want, as long as you take Bio, chem, o-chem and physics. Though speaking from personal experience (my bachelor's is in theatre and I have been finishing my prereqs since I graduated a few years ago) you may want to choose something at least somewhat useful for a job if you find you need/want to take a few years off between undergrad and medical school.
Wait, how is it that your status says you're a medical student but then you haven't even started college yet? Isn't that like some type of violation of TOS? You should probably change that.
Anyway, to you original question. No, it doesn't matter what your major is as long as you have a high GPA, you do your premed prereqs and do well on the MCATs. Now if you're wondering what classes will help more when you do get into med school that would be biochem, anatomy (if offered) and maybe physiology depending on how it's taught. Personally, I think bio majors have it slightly easier in med school than non-science majors. Now before anyone starts arguing with me and accusing me of flaming: yes, I know everyone's gonna have to relearn all the material and they do teach you everything you need to know and yes non-science kids do just as well as the science kids in med school. HOWEVER, having seen the material before makes it easier to make connections in between the different topics introduced. You're not spending your time just trying to memorize the details you can start integrating the information. And yes, I do hear a lot of the non-science kids complaining they're feeling overwhelmed having to learn this stuff in only several weeks.