My car’s fuel range meter is acting up?

[HappyHunter95]

After a problemfree period for some time, there's finally something unusual about my LC. The fuel range meter gets lower every time I fill it up. I remember the first time I filled the gas, it was showing 311 miles, it's getting lower and lower, now it's on 289 miles.

I tried pumping more in, but it didn't increase the mileage range. My current mileage is 8228. Is this normal or it's the time to take her to the dealership? Hit me with some insight!