Calif. state law on "cool off period" for New Car Purchases

I purchased a Nissan Stanza Saturday at the Nissan Dealers in Long Beach, Ca.located on Spring Street. I was not pleased with the performance of the vehicle and asked for my old car back. They were quick to point out the "no cool off period" on returning vehicles, but did not point that out to me at time of purchase. My 1987 Nissan Maxima is a much better car as far as power (V6) engine, plus it is better riding. Is there any way I can get my old car back? They told me there is nothing they can do. The car had 20 miles on it at time of purchase. When I drove it back it had 28 miles on it. They said you now have a used vehicle. Any information you could furnish me on this would be greatly appreciated. Sincerely, M.B. Church (Mch3893812@aol.com)