How long does a new car dealer have the right to cancel the contract after i have been given the car?

Read your sales contract. There will be a dealer contingency clause in there that says how much time the dealer has to demand the car back. 10 days is very common but Florida law may be different. If the time has expired you don't have to return it. You can't be forced to sign a new contract, accept a higher interest rate, get a cosigner, or increase the down payment. The dealer has to finance himself or pay the bank whatever they want to approve the loan. If time limit is not expired you must return the car and the dealer must return your entire down payment. You had free use of the car for the time you had it.