There are a few things to consider here:
1. Did you sign any agreements or supplements provided by the bank, the seller, or the seller's realtor? If so, read them carefully to see if there is any wording that would alter the standard contingency period of 17 days.
2. You have the right to see the acceptance letter from the bank in order to verify that this short sale transaction was in fact approved. Escrow could have jumped the gun with issuing the escrow instructions prematurely. Acceptance by the seller is somewhat meaningless, since the bank has to approve the short sale before it can move forward.
3. Check the wording on your original purchase agreement (and any addendums or counter offers) to see if any of the standard terms of the contract have been modified (i.e. contingency periods, contingency removals, escrow cancellation). You should also have signed a Short Sale Addendum, which indicates additional contract terms in regards to short sale transactions.
4. Have you submitted your deposit to escrow?
If the bank has accepted your offer and your contingency period is still intact (even with a bank addendum, you should have at least 10 days), then you have the right to withdraw your offer during that contingency period. If you have not submitted your deposit to escrow and you are still within your contingency period, then there likely is no recourse since they have none of your funds, unless you've signed addendums or counter offers to the contrary. If you have submitted your deposit to escrow, then escrow has the right to retain a portion of your deposit to cover their expenses if you cancel escrow. Either way, as long as you have not gone past your contingency period, then you should be able to back out of this transaction with little to no financial impact.
That said, it is not a good idea to bounce around from property to property. If you're not sure that you want a property or not, then don't submit an offer until you've completed your investigations, including ruling out other properties in the area.