It could just be that your fuel gauge pointer is bend, what does it show when you're full up. If it is over full and you don't like it you have always the option of bending the hand. Before this check that there is no extra resitance in the electric path on the circuit board. Or just leave as is. I have a nice german word for this "kaputtrepariert" - which means "repaired until it is broken" mostly for good. I think you have the saying: "if it isn't broken, don't repair it" or s.th. like this.