Not sure but from the looks of your picture of the servo arm, you have the attach points aft of the pivot point on the servo. If so you may have a problem as that will give you some negative Ackerman (the lines will tighten up as you move off neutral) which can be very hard on the servo and possible even cause it to stall out and possible self destruct. At the servo end, you want the attach points to be forward of the pivot point on the servo, just the opposite of what you want at the rudder horns. Remember, you want the lines at neutral to be just tight enough to have no sag and it will not hurt anything if the line not being pulled slacks off a bit as you move away from the neutral position.