Casting off at neck edge

My pattern says, keeping with stocking stitch, cast off 4 stitches at neck edge, then 3 stitches, then 2 stitches (twice) then 1 stitch (twice). It says to work both sides of neck edge at same time. Do I cast off only on knit rows then purl back on purl rows? When I cast off the first 4 stitches, then cast off 3 stitches on purl row I am left with a single stitch that leaves a whole in my work after next row??? Help…never decreased this way at neck edge?

Welcome to the forum!
You should only cast off at the beginning of the row. So on one side of the neck, the cast off is on the knit row and on the other side of the neck, the cast off is on the purl row.

Use two balls of yarn (or two ends of the same ball). Knit to the center, drop the yarn, pick up the second strand, bind off 4sts, knit to the end of row, turn and purl back. Pick up the first strand, bind off 4sts, purl to the end of row.