A suggestion: Restart the 'gallons used' back to zero each time you fill up the fuel tank. After a few fuel-ups you'll get to see if your gauge runs a bit high or low and by how much. Then you can calibrate the gauge with that info. Its in the manual.
If my gauge says I've burned 50 gallons, it usually takes a few more to fill up, so mine is a tad optimistic.
Rob