The Shape Top directions start with 30sts. The first row has a decrease of 4sts to 26sts. The row you quoted is the next RS row:
3rd Row: S1, s1, k1, psso, k7, k2tog, k2, s1, k1, psso, k7, k2tog, k1
Starting with 26sts,
slip one (one stitch)
s1, k1, psso (2 stitches decreased to one stitch)
k7 (7sts)
k2tog (2 stitches decreased to one stitch)
k2 (2sts)
s1, k1, psso (2 stitches decreased to one stitch)
k7 (7sts)
k2tog (2 stitches decreased to one stitch)
k1 (one stitch)
Is it maybe the slip1, k1, pass slipped stitch over that’s causing the problem? Did you start with 30sts, then dec to 26sts before the 3rd row?