That doesn't sound like a contract to me. It sounds like a unilateral condition you placed on the transaction, which isn't binding.

A contract requires an exchange of value. Unless you're a merchant who buys and sells houses, keeping negotiations open is at the seller's discretion unless they get some concrete value our of the arrangement.

Also, a seller isnt obligated to accept the highest offer even after an open solicitation for offers.

In the give-and-take of real estate bidding, generally the seller solicits offers. You make an offer, which is an entreatment to enter a contract. No contract (and thus no obligation to you) exists unless your offer is accepted.

A seller's listing can't be construed as an offer for a broad variety of reasons, and as soon as you submit a bid that differs materially from the original ask, doing so is an implicit rejection of any offer the seller might have made.