I think once you find out how much you are going to lose selling it, you will probably just keep the car.
So what, if you spend another 3k on gas over the next couple years vs. an "efficient" daily driver like a 335i. At least you'll have fun burning the gas.
That is, unless you don't like other parts of the car or the sheer act of having to stop for petrol so often. The expense of gas is not really a good reason to sell a car you just bought (especially from a dealer).
Looks like a nice far and fair deal though, glws.