What can I do if I was caught in a spot delivery scam at an auto dealership?

I put a down payment, paid my first auto insurance premium, I filled out registration papers, signed a contract with everything filled in (including APR, monthly payments and when first payment is due). The contract does not say spot agreement anywhere. I get a phone call fiver days later and all of a sudden they may not be able to finance me without a co-signer, more money down, or work out another deal at a higher APR and monthly payments.I already sold my other vehicle to a private party! The dealership hid a paragraph in my registration form stating some deal contingencies? That has to be illegal! HELP!