Welcome to the world of new home builders. Home builder contracts (in general) are the most one-sided contracts in the market place. I typically explain to my clients that once they sign the builder's contract, the builder can just about put a pitchfork in their head and there won't be much the buyer can do about it. The contracts are just that one-sided.
A few months ago, one of my clients went through the same thing with a builder. He eventually went to his bank, found that his check had not yet been cashed (it hadn't) and immediately cancelled the earnest money check he had paid the builder. Prior to this I advised him that this left him with clear liability should the builder choose to force the issue. Fortunately, the builder never even called him back about the cancelled check. I think I would seek advice of counsel ASAP since you're not clear on the terms of the contract you signed.
I would like to tell you different, but with every builder contract I've ever worked with, I doubt you have many options at this point. - Earlier today