Eltoc,

Check to make sure that your servo didn't shift. Disconnect the control rod from the rudder, turn on the transmitter, plug in the battery and test the operation of the control rod and servo. If everything checks out OK and you still need to shorten the rod, unscrew the end piece and cut off the required amount of rod using a wire or cable cutter, then replace the end piece, re-connect it to the rudder and check the operation again.