Many of the RS rows increase by 8sts but not all of them. Row 21 requires 86sts and with 5 increases, finishes up with 91sts. The ssk is indeed a decrease that uses 2sts and leaves you with one stitch. The problem may be in how the M1 is done. For this pattern you need to increase between
sts like this
(or see other similar increases on the Free Videos tab). If you use a stitch for the M1, you'll run out of sts before the end of the row.