I would not worry about it. There are tolerances involved. Both mechanical and electrical. Gauge needle calibration, float arm calibration. sloshing, whatever. The bottom line is that is not an issue of running out of gas. It does settle to read semi accurate. You would have to remove the sender and the gauge and set it all up on the bench to calibrate. There would be a chance to make it worse or damage something. The system was never super accurate to begin with.
Senders are not voltage specific. They can be used on 6v or 12v. The gauges are specific.

Other folks have their needle peg and stay pegged. This is a wiring/grounding/shorting issue. Yours works and does not stay pegged, so seems not a wire/ground issue.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn