Here is the passage again:
All of my friends wanted to spend Friday afternoon at the beach. Except
Michael, the worrier, who was concerned about shark bites, jellyfish stings,
and skin cancer.
You chose to alter the fragment so that it now contains a main clause, like this:
All of my friends wanted to spend Friday afternoon at the
beach. Michael, however, was concerned about
shark bites, jellyfish stings, and skin cancer.
Well done! You deserve that cyber sundae!