Looks like a good work in progress that george
Why don't you try using 2" masking tape stuck to the outer face of the raw carbon matting before cutting it and it holds it all together, then apply the resin to the the edges of the joint your covering, lay the carbon onto that and then apply more resin. The tape stops it coming apart and going all over the shop ! after it's hardened just peel off the masking tape. It will cut or sand nicely after that
, you can apply some more resin on the unmasked area and again after its gone off sand it smooth with wet/dry.