If you want an internal stem you cut part of the endform off and temporarily attach the internal stem to it so it can come off and go with the boat when the hull is removed from the forms.

If you don't want the internal stem you just run the strips past the end of the endform and glue the strips to each other, one from each side of the boat and then plane them down for the external stem later.

I didn't use the internal stem and stressed way too much about how bad the bow and stern looked. I really made a mess of it, I didn't do a very good job matching angles for a clean joint but after planing and gluing on the external stem you don't even see the joint.