Good for you!
Are your purl bumps on the heel flap (ie., the rows right after "Divide for the heel"), on the heel itself (right after "Turn heel"), or both? I'm thinking that somewhere in there you might have either missed a row or added a row and switched your right side to wrong side.
Or------looking at the pattern, there may be a misleading portion:
Divide for Heel
Slide the first twelve stitches onto one needle, the remaining twelve onto
another. You will work the heel on the first twelve stitches.
Knit 1 row on 12 heel stitches. This is the right side.
Work 7 more row in stockinette stitch (starting with a wrong side/purl row
first), slipping first stitch of every row.
They're telling you to start knitting the heel on "the first twelve stitches", but the way that I read this, that makes it the wrong side, not the right side. They do go on to say "starting with a wrong side/purl row first", but that's after you've already been instructed to knit the first row.