try doing a cluster self test first:
with the ignition off press and hold trip meter reset button and then turn ignition on,after 5 seconds release button and press once quickly.you should see the gauges sweep over and various lights come on.when then self test has completed one cycle switch ignition off and remove key.wait 5 seconds and then start the car.if it is a fuel gauge calibration error then the problem should be solved,if not then there is a problem inside the fuel tank with the fuel level sensor or wiring.
you should also check underneath the rear seat is the fuel tank wiring harness is not damaged.