when installing a servo
on the controller
turn up the d/r (dual rate)
set the end points to r100%/l100%
and center the trim

then power on the reciever and servo to let it center
and install the servo horn as close as possible to where the servos center should be

then set the center and end points on the controller

with many cheaper kits, the centers will change as the battery drains
or the servos strip easier