Greg, I agree with Pat in that you really need to contact a lawyer, but as a general statement, there is a concept in contract law known as specific performance. Specific performance refers to being compelled by a court to execute what you have agreed to do in a valid contract.

How that applies to your specific situation is something only a trusted attorney can answer.

I think you should be contacting a lawyer rather than posting a question on Trulia. They'll usually hear you out and answer your question for free.