Going by the gauge will not be that accurate to determine fuel consumption. Run it till empty again, refill (full), and from the milage you covered since reseting at the last fill, and the volume of fuel you put in to refill it, you can calculate your MPG.
no of litres to fill the tank divided by 4.54 = no of gallons used.
MPG = milage covered divided by no of gallons.
Then you'll know for sure that its poor on fuel!