If you check fig. 4 again, you will notice that it has 9 seams converging to a point. That is a bearcat of a problem in sewing, and I think the most reasonable thing to do is to cut away that part of the cloth and pretend it never happened. In other words, make a cutout for your neck. For this you will need a protractor. Sew up the cloak as best you can (more tips on that later) and lay it out flat. Now get a tape measure and measure around your neck. (Or, what's your neck size in inches when you buy shirts?) Use your protractor to measure your cloak angle (180 degrees for a half circle, 360 for a full circle, et cetera). Call your neck measurement N, the angle of the cloak (in degrees) A, and the radius of the neckhole opening R; then you get N=2 pi R A/360. This gives

R=57.3 N/A

after a bit of twiddling. For a three-quarter circle, A=270; with a 17" neck this works out to R=3.6". That might not seem like much, but it is enough. Put a tape measure on the apex of the cloak and draw a circle of radius R on the cloth, using tailors' chalk or such. Do not cut on this line, though you can cut out the very center of the circle if the bunched seams are giving you trouble.