It's impossible for anyone to answer your question without knowing what's in the contract you signed. If it's governed by Mexican law, you're going to need an attorney in Mexico. If the entity with which you contracted is in the US and has a choice of law clause designating a US forum, you could be subject to that state's law. Further, if you executed the contract in PA, that could complicate things further.
In short, speak to an attorney immediately and have them review the agreement, as the time in which one can rescind a timeshare contract is often very short under various state laws if they indeed apply.
The foregoing is not legal advice nor is it in any manner whatsoever meant to create or impute an attorney/client relationship.