This what Chopped Carbon Fiber and epoxy looks like for injecting Internal Fillets. The goal is to coat the root of the fin where it touches the motor tube. You need to thoroughly coat both the fin and the Tube and allow the mixture to pool creating a fillet on the interior of the rocket. Note some epoxies are thicker than others and the mixture may end up looking like "snot" and be more difficult to inject. Also if it's cold it may be thicker.