Yes, first up they do look great
When you're knitting the heel flap, are you doing the number of rows stated in the pattern, or have you had to make adjustments because of any sizing issues?
If it says pick up 21 stitches, then I'd assume you've done about 42 or 42 rows? And slipped the first stitch of ever row? That should give the obvious edge point to pick up. Then you can squeeze one or two in the 'gap' between the flap and the remaining stitches across the instep - that helps prevent a hole forming there too.
I find it's a bit of 'have a go' rather than being precise