Higher level or graduate courses are weighted more heavily than freshman courses. Your most important undergraduate year is your senior year. If you started off slowly in college, don' t worry about it. Often a good finish counts for a lot. Make sure you take a variety of courses.
Medical schools like to see a good mix between humanities, social sciences, and science courses.
Most colleges require you to take x amount of hours of humanities and social sciences anyway, so you should have this covered. Study hard and play hard. Don't fret over your grades. Remember it is just as important to learn how to have fun. Learn how to manage your time, medical schools look for this.