If you are going to run that gauge , you need to change the sending unit.
Some senders read high resistance when full, some read low. If you have a high reading sender where a low is required, you end up with a reverse reading.
To check the gauge, pull the wire at the sender and ground it. If the gauge reads empty, then it needs a low resistance when empty and high when full.
If the gauge reads full,then it needs a low resistance when full and a high resistance when empty.
What gauge is it? Maybe we can narrow it down
Sparkchaser has given a perfect example.