Help for a short sale house

I gave $10k more than the listing price for a short sale house.The saler signed the contract and mine is the only offer. The listing agent said the bank agreed on the listing price on the phone, but the bank said the offer is too lower and would order an apprisal to reprice the house. Can bank leaglly do that even my offer is $10k higher than the listing price and mine is the only offer? Is there any thing I can do or tell them to horner the the listing price?