The contract is the agreement you have with your builder to deliver your home and governs the terms of your purchase. Look to your contract to see if there is a clause that would allow you to cancel. Sometimes you can use the threat of canceling the purchase to obtain additional credits but this is a risky move. In a market where the demand outpaces the supply, this tactic doesn't work.
Builder contracts are different from your standard Purchase and Sale agreements as they limit the ability of the buyer to cancel or change terms once signed. If you are looking to actually cancel the entire purchase, then take the contract to a real estate attorney to see what you can do to get out of the contract. There is probably a penalty if you cancel now. There may not be a penalty if you don't qualify for the financing, but it depends on the terms you actually agreed to in your contract (which none of us has seen).
