" Transfer stitches around so that there are 12 stitches on the first needle, and 6 stitches on each of the other
two needles. Work back and forth across the first needle ONLY as follows:
Row1: Slip 1, knit to end.
Row 2: Slip 1, purl to end.
Repeat these 2 rows for 12 rows total, then work row 1 once more. The heel will be 13 rows long."
It sounds like you skipped a row or added a row, and yes, it sounds like it is knitted outside.
You could do that to both socks tho..... Or you could frog the heel flap and reknit that part.