Cut Hole Too Big - Uh Oh!

I have a 2021 Hobie Passport 12. I was trying to convert the round hatch in front of the seat to the rectangle hatch. I measured wrong and cut the hole too big. I have the piece I cut off, as it is in one piece. Would like ideas as to how to somehow correct so the rectangle hatch can be screwed into something secure. I was thinking maybe a piece of PVC "wood" in the hole but am unsure how to secure it onto the kayak.

Any of your creative ideas are certainly welcome!

If there is room inside of the hull, place wood or starboard around the edges to give you something to shoot hatch screws into. Make sure you have the same measurements for the outside/deck of the compass and attached screws with sealant to hold the underside board in place.