Inconsistent fuel gauge reading
 

First time poster :)

I'm not sure if there's something faulty with my fuel gauge, but would like some opinions.

I have a 2009 Mazda 3 GT hatchback. From all reports I've read online and in my manual, I have a 55 liter gas tank. This morning, my fuel gauge had the yellow light on indicating low fuel, and the computer showed that I had 20 KM remaining with the amount of fuel I had. At roughly 10.7L / 100KM, that's about 2.14 Liters of fuel remaining in the tank. The low-fuel warning light actually came on when I had about 28KM left (according to the trip computer).

I filled up until the nozzle clicked, then filled a little more slowly until it clicked again (I could hear the gurgling sounds in the tank so it was getting pretty full). The fuel receipt showed that I had put in 44.8 Liters of fuel.

With the 44.8L I put in and the (roughly) 2.2L already in the tank, that brings me to 47L total. Now here's the question: Where are those extra 8 Liters of fuel I should have to bring it up to the 55Liter max? Is it possible that the fuel gauge is not reporting the correct amount of fuel remaining?

I always reset the odometer when I fill up. When I first got the car, I would see the odometer read between 450 - 480KM per tank/fillup. Now when I cram as much fuel in as I can, the odometer shows 380KM until the low fuel light goes on. I'm thinking that the low-fuel warning light is coming on way before it should, but how can I be certain?

Thanks!