Without knowing all the facts and your location it's hard for me to make a proper comment, but will say when you sign a contract it's binding unless contract was signed away from the dealership premises in which case there is a cooling off period.

Some dealers will let you walk away " very few " while others will keep your deposit if there was one in hand ?

If the contract has to be altered in any way you have a right for a refund ?

If there is no deposit in hand by the dealer, 99.9% says simply walk away from the deal

If you feel your purchase was misrepresentation send me an email with all the details for me to supply you with a more direct answer.