If you bought a brand new car and your not happy with what they did can you take the car back to the dealership?

No. Once you sign the papers, there is no buyer's remorse law (the 3 day rule) on vehicles. Sure, they would probably give a good deal buying your a used car with little mileage on it. But it is a used car the minute you drove it off the lot and probably lost several thousand dollars worth of value.