3.5 over your last 40 isn't impressive. From a 3.3, every grade you get that isn't an A is a step away from med school.
Think bigger than "SMP or what?" here.
Location: If you're in California, just assume you need 2+ years of additional work after finishing prereqs from a 3.4. That might mean an SMP like Gtown plus a gap year, or it might mean traditional grad study with pubs. The less competitive your state, the less you need to do to account for a 3.4.
DO willingness: If you're willing to consider being a DO, that's by far the fastest path to becoming a practicing physician in the US. Do not look at Caribbean schools as a viable option, that's just a joke.
Access to more undergrad coursework: If you can conveniently take more undergrad, then you can avoid the expense and risk of an SMP. You don't mention if you've graduated yet. If you haven't graduated, look into adding a minor or 2nd major to extend your undergrad program. If you've graduated, then it's less convenient and more expensive to keep taking classes. Berkeley Extension and Harvard Extension are good examples of flexible postbac options for GPA redemption.
Resources and seriousness for the MCAT: The majority of MCAT retakes result in a lower score. Only pursue a retake if you're going to dedicate substantial time, energy and money to the job. Don't use practice tests to gauge your readiness, because you'll never see that content on the test. Use comprehensive content review and do a million quizzes/problems.
Timing: The year you apply to med school is less important than the month you apply. Plan all of this around being ready to submit a complete and compelling app on June 1. "Losing" a year in favor of securing your maximally competitive app is not a loss. Being ready to apply in early summer means you have your best MCAT score in hand on June 1, which means any MCAT retake happens in April, May at the latest. You also need to have financial resources in hand for secondary fees and interview costs at the time you submit AMCAS.
Baketime: If you do not yet have experience with real responsibility, where your mature decisions result in your ability (or not) to pay rent and in the success (or failure) of a large team project, then you should look for such experience before you pursue med school. There's too much competition for med school to assume you can get away with just being a mall rat gamer who never spells out words like "because". That describes a typical 21 year old, which you can't afford to be.
Best of luck to you.
