when I am racing my truck the servo when turned right stays a little right and when I turn left it stays left so I am having to adjust the steering all the time cause it wont center. How do I get it to center all by itself when I let go of the wheel on the radio ?

I am using a 300 spectrum receiver
rx3s radio.
losi servo and spectrum 6040 servos having issue with all units could it be the radio settings ??
any help or ideas Thanks