Can you return a used car after having it for a few months?
No, you cannot return a used car after having for a few months. In most cases, you cannot return a used car at all once you have purchased it.
What makes you think you can just return a used car? You are referring to the Cooling Off Period or Buyer's Remorse Law. That law only applies to unsolicited sales and not to the sale of a car. Unless the seller agrees, you cannot return a car you have purchased. You bought it so therefore it is your car.