I had a sales rep come to give me an estimate for 2 replacement windows, new gutters, and new vinyl siding. He gave me the quote and I accepted his offer. We signed a contract and I gave him a check for the full amount. Several hours later he called me to say that his numbers were off by about $8000. He wants to come over right away and have me cancel the agreement. I told him to call me tomorrow. Do I have a right to hold him to this contract?