^ Definitely take and get As in a few upper level science courses. MCAT is fine.
Get involved in some interesting and meaningful extracurriculars. If you have the same cookie cutter ECs that most candidates have, you will blend in to the crowd when your goal is to stand out (in a positive way). More and more applicants are taking gap years to bolster their applications, you might have to do the same. Just remember to be productive during that year. Pair this with high quality writing on your essays (start early and get a friend who is a very strong writer to review with you) and you'll have a good shot.