Don't worry so much about failing and be confident that you can pass if you try as hard as you can during your basic science years... McGillGrad has given you excellent advice... just keep practicing Step I questions in your free time... especially when you are actually studying that subject in school. Generally speaking, the curriculum in the caribbean is heavily geared toward passing the Step I... so you should be able to do it.
One more point... I don't know your exact motivation for medicine, but if you have problems taking tests (which I'm unsure if you do), you're going to have a long and tiring road ahead of you in your quest to become a licensed attending physician.