2014 C gas gauge wonky

My gas gauge isn't right. Halfway through a 600 mile car trip, it said I had 3 bars... which should not have happened as I started with a full tank. I could only put 3.5 gallons in before the pump stopped. It said 4 bars less than 2 hrs later and the pump would only let me put in 2 gallons. I got home two hour laters to now having only two bars. I have owned this car (32K miles) for a year and a half, never had one problem till now.

Any ideas, or directions specific to this make and model? I am going to try disconnecting the battery tonight, but I am not holding my breath that that alone will work.

Also, I have already tried the reset Odometer thing that is mentioned in several threads. Five or six times. The instructions are not worded for a Prius C, so all I end up doing is changing between TripA/B/Odo or staring at the Power On screen. Nothing happens. I have reset the maintenance notice before, so I get the concept and know how to do it when the directions are for my car.