There is an error in the chart on knotions:

Rows 3, 5, 11, and 13 have an extra K1 at the end of the row (before the purled edge stitch), there should be no stitch there.

All even rows (WS) except 4 and 12: K1 for the edge stitches and purl the 15 middle stitches.

For Row 4 you would then K1, P10, P2tog, P1, K1

For Row 12 you would K1, P1, P2tog, P10, K1

Hope that helps.