It doesn't matter what your major is. Just choose something that you enjoy and will do very well in. Then, make sure you take all the pre-reqs, like o-chem, bio, etc. Your school should have a health careers-type office that can tell you what the required classes are. Then, take these classes and get A's. If you don't have time to fit all these classes in, you can always take a year of post-bach classes. That would not have any negative impact on your application. Also, taking a major that is a little unusual (that is, non-science or non-bio) can be a positive thing. It can make you a little different from the thousands of applicants each school looks at.
Be sure to look into the health careers office at your school, early and often. They will be an important resource, not only for practical services like a recommendations file and school information, but also for advice. The counselors there will often know people on admissions committees on a personal basis.
One last thing: Don't be afraid to drop classes you're not doing well in. Obviously, be reasonable in the amount that you drop. But it is much better to take a little longer to graduate than to have a C in an important class. I think the AMCAS application does ask you to designate courses which you have dropped, but, if it doesn't show up on your transcript, then there's no need to tell. :wink:
Good luck and enjoy your undergrad. I miss those days!