Fuel guage reads 50% less?

[Blazing angel]

I've got no idea how this actually happened, but in my 1999 Cvic SE Sedan (d16Y7, no Vtec), the fuel guage goes 50%. For example, 50% is actually 100%, and 25% is actually 50%. It's like the guage cannot pass 50% on the meter. Furthermore, when i fill it up, it slowly rises to 50%, like the power/amperage is low.

What should i check? The Fuel module in the tank? The cluster?

Help

(Thanks in advance)