Optional: Work one or two rounds of Single Crochet before beginning the edging. The instructions say to work into next 3 sc - if you have not worked the base round(s) of single crochet, then you will just work into the next stitch on your item. Try to space as evenly as you can, but don't worry if you have to maybe skip an extra stitch or only skip two stitches between picots to make it fit. It doesn't have to be perfect!
Multiple of 3
Ch 1, 1 sc in next 3 sc * ch 4, sl st in first ch, 1 sc in next 3 sc*. Repeat from * to end, fasten off.