Following this repair method will result in a very week spot in your hull that could pop out under severe weather conditions. Don't do it! Do it right or hire it done by a professional! Doing it right involves grinding the hole back at a 12 to 1 ratio. That means that for your 3/8 inch thick hull the outer edges of your ground out area will be 4.5 inches away. Then gradually build up with larger and larger pieces of fiberglass roving until the final piece is the full 10 inches diameter. Actually Ferenc Mate says in his book "Shipshape, The Art of Sailboat Maintenance" that if the hull is greater than 1/4 inch thick then the ground out ratio should be 15 to 1 but everyone else that I've read recommend only a 12 to 1 ratio.
The rest of Sabreman's recommendations are quite good. That is cleaning the area very well, etc.
Yes +1 on this.
You HAVE to "taper" out the hole both sides to get good ahdesion of fibreglass to hull. 12:1 is a minimum to spread the load.
when "laying up multiple layers of glass yo can lay them up in mulitble layers in one hit! Polyester will try quickly so ensure that you do this quickly and compress as you go to remove air.
It is also important to ensure that is the hull is layed up using epoxy that you use epoxy for the repair. I suspect it will be polyester and thus polyester, vinylester and epoxy resins will be ok.