It depends on the terms of your agreement.
If your agreement contained an express condition requiring you to come up with the deposit before a certain time, and you were late, then the seller can rescind.
If your agreement was general, e.g. "Buyer shall provide earnest money of $XXX," then I certainly believe that providing the earnest money check the day after you signed the contract is reasonable.
If you feel strongly enough about it, consult a property lawyer, who may advise you to place a lis pendens notice on the property. But, in this market, with a 24+ month inventory of homes, you might be better off avoiding the aggravation and look for another home to purchase.