If still in the water. Add length to your stopper rope and drop the board out the bottom. Then Keel Haul the offending DB and rope back to the stern and retrieve. Then you will have the fun of having to unstep the mast to get the DB back in.
Hope you did not hurt the center board. I would have put pressure and leverage on the board and pushed it up and out. Never hammer. Where on lake MI are you. I lived in Berrien Springs in MI 12 miles form the lake. Glad to be in California.Success!!! Went to Ace Hardware and purchased a piece of flat steel about 7 feet long and 3/4 inches wide. We could see the the stuck piece toward the front of the daggerboard. Don laid under the boat and directed as I placed the steel down the side of the daggerboard on the offending piece and kept hammering until it finally dropped out the bottom. Took about 1/2 hour and cost $8 so we're in the business of sailing again.
Thanks for all the suggestions.