You won't be in trouble. Did you try to do it online? Much better to do it in person as far as getting denied goes. You will have to use a different payment method for that vendor or a different name and phone number for mg. Just know that if you use a fake name, you can't get your money back if the clerk makes a mistake you don't catch or anything else that could go wrong.
If the vendor doesn't have alternative payment methods, maybe get a friend to send for you? People get denied all the time (especially online), so don't worry about being in any trouble.