fuel guage off?

I think it's too early to tell. The best way to determine mileage is to fill the gas tank until the pump clicks off once and reset the trip odometer. At the next fillip, fill until the pump clicks off, then divide the mileage on your trip odometer by the number of gallons you just put in the tank. With the Gen II Prius you have, the gas tank has a rubber bladder which sometimes doesn't expand fully when you fill the tank, but over the course of a few fill ups, it will average out. Use only regular gas.

The 42 MPG you're reporting could be your driving style or the weather or the road conditions (mountainous, for example), which could reduce mileage.

 

It is much too early to tell. For now, judge MPG only by the MPG display, not by fuel 'guess' gauge bars. Ignore the first refill. With your model year and its fuel bladder, don't wait until the last bar.

After your second refill, compute MPG the old fashioned way (miles traveled divided by gallons refilled), and if it seems low, start filling out this questionnaire: Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new

 

42mpg is not unusual in the winter with a prius if you don't have an engine block heater or have blocked cold air from entering the engine compartment. Short trips are a killer as well, as are heavier stickier winter tires if you are smart enough to use them in the winter. (Prius cannot be 'rocked' out of deep snow like a 'normal' car)

try to use the same pump every time at the same gas station, only buy gas from gas distributors found on toptiergas.com for cleaner running, longer-lasing more fuel efficient engine. Chevron will give you the best mpg but is not avail nationwide so I have to settle with Shell (still very good) where I live.

 

42 MPG sounds ok, though you will be able to improve this with warmer weather and a bit of practice driving a hybrid.

I assume that your real concern is that 4 pips should be at least 4 gallons, so you're thinking that you might be only getting 105/4 = 26 MPG or less. Don't worry, the pips on the gauge aren't accurate enough to infer that. Just go with the displayed MPG until you can average your true fuel consumption over several tanks full.