My gauge was spot on when I did it in stockinette but the size per side when I actually made a pentagon was 4.5 in (not the 5 in as recommended for the XS). Each time I completed a pentagon, I wrapped it around myself. After finishing the fifth, it was actually long enough to completely wrap around my shoulders but I couldn't figure out how to move the sleeves around so I made the sixth pentagon and just cinched the collar tighter (the button is way up on the collar, not near the end as in the VK picture).
I really recommend going a size smaller with smaller pentagons and wrapping it around yourself as you go along. It was a really satisfying knit but you do have to make some modifications.