Estes Thor Agena B Build Part 28 Tunnels

You should extend the tunnel lines over the lip of the lower BT-60 body tube.
This will give you a centering tick mark at the end of the half round.
When the half round is glued down, it'll cover up all of the pencil line except for this end lip tick and the line below the end of the tunnel.

Because the body tube was already primed, you should sand off the primer down the pencil line.

Use a sanding block and redraw the line after it is sanded off.

The tunnels were cut just a little long. The pencil line is the cut line.
After the glue dries, the tunnel end will be sanded down and flush with the end of the body tube.