Not knowing how your contract was written will make it difficult really help. Check with your agent, and with any legal issues you should check with a Real Estate Attorney.
If you have signed a contract then Buyer and Seller have agreed to terms in writing. The Contract is contingent upon the seller's lender approving the short sale. If you do not agree to the terms that the bank is willing to do, such as if they don't release you from the liability, then you can choose to not agree to those terms. Some banks will release the lein so that you can sell the home, but do not release you from the liability. This term could be one that could get you out of the contract. But if the bank may agree to everything. You should check with a Real Estate Attorney to see what options you have.
Ron & Brenda Cunningham
West USA Realty
** Recognized in the Phoenix Business Journal as "One of the Top 50 Realtors in the Valley" **