Gas Gauge

So, I thought I had about a 1/4 tank of gas left from the last time we were out. Pulled into Table Rock Lake last night, filled up before launching and the gauge (analog and digital) are only showing 50% fuel. I put about 21 gallons in when I filled up at the gas station. Is there any thought that the tank could vapor lock or anything and not actually have gotten full at the gas station?

I open both caps to fill to give the displaced air somewhere to go. Otherwise the air escaping through the fill hole spews gas with it and cuts off the nozzle.

Make sure there isn't wax build up or debris on the vent. Had that happen to me once