You might want to go back and check that you have the correct function assigned to the correct axis. Also, calibration is for all axes, so make sure you move your throttle, stick and rudder competely to all limits.
If all that is correct and your plane is turning without any input in a gunner position, increase the deadband a little on rudder or aileron axis. That should not be needed, though. That would indicate a problem with your joystick.