Is there any OBD2 App that shows the true gas level in the tank?

I only ask since my gas light comes on after 380 miles, and I always ended filling up around 8.5-9 gallons. My trip meter indicates I have 0 miles when clearly I have 2.9ish gallons remaining, or one would assume so. I have heard horror stories of people running out of gas and not being able to restart the vehicle due to an issue with the battery.

 

I don't know of a app that shows the gas level in the tank.
However, even if there was, it would most likely show the same level as the gauge, as the sender unit would probably be the same unit.

I've heard that the reason that there is about 3 gallons left in the tank, is because the pump is submerged in the fuel to keep it cool.
So, it's not a good idea to run it lower than that anyways.