You can submit an offer up until closing; however the seller is bound by the terms of the agreement he/she has already signed. It is a contract and unless the buyer does not perform under its terms/is in breach, it can't be broken.
Keep looking and as prior poster suggested, have your agent keep an eye on it. There are generally two contingencies that have to be cleared - inspection and mortgage. Things can and do happen causing deals to fall apart.
Good luck and best,
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