A couple of things. Phil is correct that if you are trying to find the center point and you get to the end of the allowed adjustments in the servo offset program, then you need to undo the screw holding the servo horn to the servo, lift it up and move it one click (15 degrees) in the appropriate direction...
As for your program, I am not 100% sure what the end statement does with the HSERVO subsystem. If it were me, I would try:
The end statement may work fine, but if I were having problems, I would try changing it like I mentioned.