This depends on your contract. Some builders allow you to reserve your home for as little as $100. Some require an earnest money deposit of 1% or more. Many contracts are drawn up differently and it would be unwise to take any suggestions about your obligations from this forum. If you signed a contract, it should be clearly spelled out in there. I'm sure the contract is long and difficult to understand at points, but you will probably have to find it on your own just to be safe.
Sorry to be a downer, but reading the contract is the only way to know for sure. Good luck!