Fuel does expand and contract with temp. as well. When I would fill my Civic on a hot day in the summer the pump would click off noticeably early, and I could easily get another gallon in beofre the "actual" click off point. What time of day did you fill up at? I always do better at night or first thing in the morning. A HazMat tech at work told me gas can expand as much as 1/8 or more its volume depending on the temperature.