i work on this basis
youve paid 2 years worth of finance, this has paid for the car, the next year will pay the interest. if you hand the car back now, you are in no better of a position than oyu were 2 years ago, if you hold out until the end of the agreement, you will have a car that you own that you can use as as deposit against a new car
unless you bought in on PCP, in which case, you can p/x it through the dealer and they should paty you enough for it to pay off the finance company