Is it possible to pump 13.03 gallons into it?

I am confused as this would make my mileage about 43mpg for this tank, yet ~70% of my trips had a mpg reading of over 50. 25% were over 54mpg. The mpg display showed 49.5mpg for the tank.

Are the specs for the gas tank wrong?

Is is possible that the mpg readings would be that far off?