Does ca have a 3 day return policy on cars?

NO. There is no such law in any state. The law you are referring to, sometimes called, Cooling Off Period, or Buyer's Remorse Law, does not apply to the purchase of an automobile. It applies to unsolicited sales. Things like door to door sales, telemarketer sales where you did not initiate the call. This myth just will not die. If you bought the car you own the car.