Be careful and don't let the fuel tank get too low. I don't recommend driving until there's very little fuel left in the tank as that can cause the electric fuel pump inside the gas tank to burn out and they are in the range of $450-$650 + to replace. Ouch!
What causes this to happen is the fuel is actually used to cool the electric fuel pump it is immersed in, by helping to disperse heat. When that fuel gets very low, it exposes the electric fuel pump to the air and it heats up, which can cause it to fail. For this reason, I recommend refilling the gas tank at about one quarter of a tank in order to help the very expensive electric fuel pump to live a very long, low cost life.
Yes, onboard fuel economy computers are notoriously inaccurate, as you have seen with your own eyes. If and when the fuel tank is low, be very wary about trusting those onboard fuel economy computers or you could be left stranded alongside a road somewhere with your car out of gas.