Can a dealership take your car if financing was approved already and the car was signed off on with title and ownership already belonging to us. The dealership made the error and want the truck back.?

Technically you are not the owner of the vehicle until you have paid every repayment it is the property of the finance company.

Just because the vehicle is in your possession does not mean that it is yours as the contract that you signed has not been forfilled (the paying in full part)