Sam, bummer, thats a tough one to fix sanding through the cap. Did you pre-sand the top before the black coat went on ? I always skip the pre-sanding for the reason of not sanding through the cap.
I'd suggest try and get some black stain over it and try and make it blend in. That light ring around it makes it pretty obvious.
I'd also try and steel wool off the stain on the top binding and it will be easier to clean next coat