Disclaimer: The materials provided below are informational and should not be relied upon as legal advice.
If you had returned the car with over mileage, the dealership may have come after you for mileage charges. Now taht you have purchased the vehicle, if you return it the dealer may come after you for breach of the purchase agreement. Look over your agreement to see if there was a cool off period that would allow you to return the car without any penalty. Otherwise, you may need to speak with them and see if they would be willing to somehow work out the situation. You should consult your own lawyer to protect your legal rights.