It does look like you still have a gap between the side flat of your barrel and the lock bolster. They need to mate in order to keep fouling from going into the internals of your lock. This photo shows the fit you should have.
The wood on this rifle is taken back to the breech like yours. But, as you can see from the inletting black, the back of the locks fence mates to the wood. Your lock plate is pretty far forward, probably due to the location of the touch hole. It's not uncommon for the rear of the fence to be a little forward of the breech though... usually the wood is left as in Mulebrain's photo. You could carefully fit and glue a piece in. The two pieces will need to mate perfectly, and you should stain the surfaces before gluing. Then, if the finished rifle if stained a little dark, and that area is even a bit darker still... It's notice-ability will be at a minimum.