How much should I ask for?

I am selling my Scion Tc and Kbb said its worth 12750, but thats too low cause I paided 18800. Thats a 6k loss and im not taking that. I have the title. the car is paid off, its a 2007, marron, its has a wing and the aerodynamics, 21xxx. I'm trying to get money back from the dealer cause the car i want to get is about 12,000. How much should I ask for?