I need to read your contract to know what exactly is

But my guess is that you need to close it ( actually buy it) within 60 days. If you cannot do that and are still working on it, you should request an extention with an addendum. Otherwise, if the seller can find another buyer with a higher price, s/he can take your deposit and sell to the other buyer. Though, if you don't release him/her, there will be lots of trouble for her/him.