The fuel gauge needle does no go to full position when tank is full and then reads a lot closer to empty then the actual fuel level. It indicates about a quarter or less when it is closer to half. Is the problem in the gauge or the tank?
it would help to know if it is a new or old problem.
You need to look at the fuel level sending unit. This is a float in the tank that sends a voltage to the fuel gauge based on how full or empty the tank is. It may be part of your fuel pump or it may be separate. A mechanic can look up the voltage specifications and then check the voltage on the wire that goes from the sending unit to the gauge, to see if the sending unit is sending the wrong voltage or the gauge is wrong.
This may sound silly but are you sure the tank is full when you think it’s full? There can be other problems that result in the gas pump nozzle shutting off before the tank is full.