No, there is no grace period in which you can turn the car back in. It's like putting a gun to your head and pulling the trigger - once it's done, it's done.
However, at least here in GA, cars are sold with "bailment agreements" which is also referred to as "spotting cars". IF this happens and you can't provide what they want, they can either keep the contract as it is OR take the car back. If you really want out of the car, call their bluff and tell them you can't provide the paperwork they want. They may or may not proceed with the deal.
Here's a little story from a local consumer guy (who's an idiot, but at least this is accurate):
http://clarkhoward.com/clarkmedia/tv/car_spotting.html