How do I get out of my car purchase contract?

About a week ago I went into a dealership just to look around. Saw a car I liked and in the process of what I thought was just seeing what payments would be if I were to buy, before I knew it I was signing a contract to buy a DIFFERENT car. Yes I know i am the kind of gullible guys car dealers are just waiting for, but once I got home I realized there is no possible way I can afford this car. I called the dealership back and the response I got was I signed a contract there is no way out. What can I do? I have not signed anything but the agreement to apply for financing (which was approved some how) and they want me to come "fill out the remaining paperwork and take your car home" I also think I may have already signed over my current vehicle as a trade in and they still have my title. Please tell me there is a way out of this!!