Yikes, was the 100 Tarpon or one fish of 100lb?
Sounds like you had a great time. Mahi Mahi are great fun on flies. We all lose fish from time to time. If you find its happening a lot then make sure your hooks are sharp - always carry a sharpener. When you get a hit, try not to lift the rod. Set the hook hard with your stripping hand. Four or five really sharp pulls should do the trick.
Then you can get a picture too
Thanks for the report!