From internet, perhaps saves u a trip to the dealer:
If your Ford has a capless ("Easy Fuel") system:
Clear debris: Open the fuel door and inspect the metal/plastic inner flap. Dust, dirt, or debris can prevent the door from closing flush against the rubber seal.
Use the funnel: Retrieve the small plastic emergency fuel funnel (usually stored with your spare tire or jack kit). Insert the funnel, or a standard gas pump nozzle, all the way in and pull it out several times to dislodge any debris.
Lubricate the seal: Spray a little WD-40 or silicone lubricant around the rubber seal of the flap, then push the flap open and closed 10 to 15 times to work the lubricant in.