My bit, because Jon's idea will be very hard with a shape like that. Duct tape across the outside to cover the hole. Feather out the hole from the inside heaps bigger so it looks like a shallow pond slowly drying up, all those layer are wide around the edges ..... only looks like that if it's laid matt construction, if it was just sprayed chopped matt into a mould, no real layered look, but still feather it out over a large area . This is important to make it bond to the substrate and not just crack around the edges and pop back out in the future.
Next is the method Jon put forward, cut lots of pieces, each slightly larger than the last, the shape of the now feather edged hole (it should be larger now than before) till you have enough to build the patch back to the original thickness.
You might need a new layer of duct tape, the sanding probably wrecked it, from the inside, a layer of resin over the sticky side of the duct tape and up the edges, add the smallest piece of cloth matt and dab more resin in until it seems to disappear, a layer of resin over that and repeat until it looks thick enough to allow the piece to be sanded flat. By this time it will be getting fairly warm around the patch, clean up the brush and resin pot, have a beer and congratulate yourself on the progress so far, this is to give the resin time to set up and stop you fiddling with it and/or, trying to take the tape off and finish the job all in one go
When you think you have had enough of rest away from the job, peal the tape off the outside .... and head back to the beers until tomorrow.
When the fog clears from the night before, sand the inside till you are happy with the finish, sand the outside to get feathered edges and repeat the inside repair process ..... if you sanded it well enough when you did the inside, there is already that feathered edge, so just a light sand and the coat of resin with the talc to make it white enough to blend in .... now leave it alone, the more you mess with it, the more you'll need to fix later ..... the next day it will be fine to do what ever you want to do with it, sand it and paint it or just leave it how it is .... enough words Jon?
T1 Terry