You are probably correct that it is fuel cap related. Was the fuel cap ever off when the engine was running or not screwed down tightly after you filled up? Either will cause that diagnostic code.
By the way, you can display your own diagnostic codes without the need to go to Autozone. Simply turn your ignition key on-off-on three times within five seconds (not to the Start position) and then leave the ignition switch in the final on position. After several seconds, have patience, any stored codes will start showing up in your odometer.