My CK30 is almost three months old with 17 hours. The first time I filled it up full it stayed there for a while. Thought it was stuck. Finally it came down to about two thirds and read good the rest of the way. When mine is at 1/4, the tank will take five gallons and be topped off. Sort of makes it easy and gives me a good cushion before running empty. I also use the hour meter. With varied jobs, mine seems to use a gallon per hour.
If yours it at full all the time, even when the fuel is down, call the dealer. You may need a repair. Other members have posted that their gauges aren't always accurate but yours seems bad.