terminating a short sale contract

Since the contract is final and binding, you can lawfully exit the contract only if the contract allows you to do so.  Typically in a short sale contract, the only ways to exit are (1) if your mortgage does not come through, (2) if your inspections find significant problems with the house and the bank or seller will not repair, or (3) if the approval of the seller's lender for the short sale takes longer than the contract allows.  I don't know the details of your particular contract, so this is just a guide to what it typically there.