To replace Ca hinges, it was suggested earlier, cut them and do new slots and put in new hinges. The faux-paux is a minor one, shouldn't hurt anything. If it bothers you. Just peel some covering off the rudder at the tip. Glue on a piece of balsa the thickness you need as long as the top of the fin. Put a small piece of covering on it. Voila you have made an airodynamic counterbalance. It would look just fine.

Mark Shuman