Possible issue with fuel tank?

Hey everyone,

I've been a prius owner and forum lurker for past 3 months but did not have a need to post until today.

Sorry if this has been asked before, I did not find this specific question. If it was asked, please point me in the right direction.

Here is the background story.

In the 3 months since I bought the Prius brand new I managed 5500 trouble free miles. I have filled up the tank 10 times before today, and everytime it was 9 to 10 gallons after driving average of 500 miles on the tank.

Today's fill up appeared to be the same as well, 516 miles on the trip odo, I had 2 bars left when I left the house and that got down to last bar of fuel when I got to the gas station 10 miles later. I expected another 9 or so gallons. The pump stopped at 5.7 gallons. I figured the pump just stopped early due to some issue with the pump, so I had the attendant restart it (full service in NJ) but it stopped again .4 gallons later. At that point I did not want him to go any further.

Now, i know about the bladder tank and how it can shrink in colder weather but it was low 80s and sunny today, about same weather conditions as when I filled up 9 gallons last time. When I started up the car, the fuel gauge showed all 10 bars

My questions are:

1. Could there be an issue with the tank now accepting less fuel for reasons other than much lower temp.

2. If the issue was with the pump displaying wrong amount of fuel pumped (where more fuel was really pumped than was displayed) will me putting in extra .4 gallons cause any issues with the tank due to overfilling?

Please let me know if I didn't cover any relevant info.

Thanks
Kris