I noted this in another thread but I think this is the better place.
In my case, it was hitting to top-left part of the castle maybe 2/5 times. I also thought the catapult was too powerful but that's not the case.
I followed Lloyd's advice and it was an easy fix for a newbie like me. I now understand it might be hard to get this adjustment perfectly out of the factory for each machine as the right position is quite precise. A little on one side and the ball could hit the red lamp. A little on the other and it would risk hitting the top-left castle tower.
In any case, once in the wire ramp in the perfect position, the catapult works 100% of the time without hitting anything.