Draw inward towards neck the four vertices of the extruded part which were not grouped with the 5s of the last step. Like so:

Join these across to close up hole, so that four become two:

Lower collar back into place like you did earlier, and fit it the way you like. Next page we thicken the edges of the collar around the neck like we did with the sleeve. You probably could do that now without my help, but I'll include that as the last step.