hi jerry,
I've done similar repairs (thought not in the same location) on cats in
the past, but take my advice with a grain of salt; im no expert on
fibreglass and there are plenty of people in this group that will give
you better advice than i will.

Is there an access hatch where you can get to the inside of the hull?
If so, leave it open and in the sun for as long as you can, do try to
dry it out. Resort to hair dryer(s) where necessary. remove the gel
coat/paint if there is some with some rough grade sandpaper and
generally rough up the area so there will be something to 'bite' on.
use a bit of mat if you have some, i find its easier to work into the
corners than chopped strand. build up a bit of extra interenal
strength if you like by making an extra bulkhead or bulkheads. just
use a bit of cardboard or whatever across the hulls, then glass over
it. This adds plenty of strength.

Not sure what to do on the ourside. On my boat i glassed it there too,
but it sure looked ugly. Im not much of a hand at glassing, and i cant
say im porud enough to sand/gelcoat/paint afterwards. this was more of
a working repair for me and it worked just fine.

Shaun