I've enjoyed this pattern, but have hit a snag, if you will. I'm at this point in the pattern:All you need is 15 stitches, spaced evenly along the edge of the heel flap. If you slipped the first stitch of every row on the heel flap, you'll find that those double height (i.e. two-row tall) stitches are a nice guide for where to pick up.
Re-establish Round and Create Gusset:
Knit all heel stitches. Using that same needle, pick up and knit 15 stitches along selvedge edge at side of heel, using slipped stitches as a guide.
I've picked up 15 stitches, but still have about 9 stitches to pick up before I get to the 33 stitches on the holder. In the directions prior to shaping the heel, I did 21 rows of stocking stitches, so it seems like I should be picking up at least 21 stitches.
Hope this helps!