First of all, don't even consider the Caribbean until you get your MCAT scores. Once those come in, with your 3.0/2.9:
MCAT < 24: Very, very little chance. Extracurricular activities wouldn't even help. Those are low stats for the Big 4, period.
MCAT 25-29: There's a chance, but it's far from guaranteed. You're GPA would be significantly lower than the average and your MCAT would be barely higher than the average. Apply early, hope, but not guaranteed. AND...if this is the best you can do on the MCAT with all the prep time you have, and considering the GPA, you might want to acknowledge the fact that even if you get into a Top 4, you won't be a star down there. So even if you do get in, realize that you'll be taking on a lot of debt for a degree in the Caribbean and probably a lower tier residency. Maybe just do DO in this case.
MCAT > 30: Good job. The best news here is not that you can get into a Big 4, it's that you're competitive. And for god's sake, you're only 21. Get a Masters...do very well in a master's program. You'll probably have to get a job afterwards for a year building a really good resume (think research). Bottom line, you can be 24 and half-way through a second-class Caribbean school destined for Family Practice. OR you can be 24 and getting into a US school with absolutely nothing standing in your way.
Just my 2 cents...