At the risk of getting in here late.... You made a simple repair painfully difficult to observe....I know I've been there.
The whole repair could be made in a couple of hours (two one-hour sessions)....with planing.
I don't understand the scheduled lay up (all that thickened epoxy
and then a couple of flimsy layers of cloth), boiling up--a PITA to sand, etc on a simple repair. Since it's an area that doesn't need compressive strength I would: After a long drying out, put down a drop cloth, chamfer the edges 20:1 (thickness of bottom skin) with a 50 or 60 grit grinder, blow out the dust/debris, wash out with acetone, wet out the area with unthickened epoxy, then in the same batch add enough bonding thickener to get a no sag peanut butter
consistency with bonding thickener get it in there with an acid brush and butter up my pre-prepared
core material press in in there till the epoxy squeezes out. put a sheet of plastic on my pre-prepared
piece of 1/4" Masonite or plywood and then wedge my precut
piece of lumber
between the floor and the repair. A helper would be useful for that.
After cure, remove backer, wash with scotch brite, dipped frequently in a large bucket of water, wash with acetone, sand with 80 grit, paint
unthickend epoxy on the repair, and coat your pre cut layers of fiberglass
, let it cure slightly and press on and squeegee out the bubbles. large to small pieces to cover your chamfered edges. put your board back up. Or just read: