Welcome, the easiest way to be sure is pull the deckplate(either 6-8screws or a quick turn pull patch), normally the one closest midship.
There is likely a capacity plate on the tank label, use a flashlight and take a towel to wipe any crud obscuring it.
If its not there or you cant find it somehow try and measure the tank LxWxD in inches, if its not a V tank, and divide into cubic inches , about 231 to the gallon.
normally these size boats had min 55 gallons i think and many had 80-95.
see this thread after you know for sure and post your result.
also your sending unit will probably be right there too if you need to change it.
fist clean the contacts and connectors well and try again.
If the fuel level is "going up" the circuit is getting better/worse and resistance
changing so Reading moves. sunk/stuck float normally would give almost empty reading or nonmoving reading. try that first.
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