I believe my answer and your follow up info crossed paths. I will repost my answer below, so that you have it in sequence.
If you signed a release, in exchange for payment by check in a certain amount -- and assuming that the check is good (which it may not be, so you may want to contact the bank on which the check was drawn), then that's an enforceable agreement, and your return of the check would be a unilateral rescission of the release agreement.
A unilateral rescission is only enforceable if you can prove your mistake, and the court determines that the mistake was made in good faith, rather than as a means to undo the contract. Note: "rescission" means to "undo" a contract.
You would have to send a letter stating that you are rescinding the release and returning the payment. After that, you may have to sue the contractor to enforce the rescission. Whether or not you would win or lose depends on the evidence available to prove your mistake. I would have to review literally everything involved in the transaction, from beginning to end, before I could give you a competent opinion about your chances of success.
But, the direct answer to your question, is, "yes," by returning the check, and providing a rescission letter, you can undo the release.
I hope I've answered your question. Please let me know if you require further clarification. And, please provide a positive feedback rating for my answer -- otherwise, I receive nothing for my efforts in your behalf.
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