Re: First centerboard vs. rock experience
There is a product called Marine Tex which is designed for underwater repairs to fiberglass as well as many other great uses aboard a boat. If you have no major water intrusion into the board, I'd just use the MT to build a patch which can be easily sanded and fared to become a perfect repair. I would liberally use acetone to remove any moisture before patching.
"Any idiot can make a boat go; it takes a sailor to stop one." Spike Africa aboard the schooner Wanderer in Sausalito, Ca. 1964.