Pattern reads:
cast off at each side on alt rows 2 sts (2) times and 1 st (4) times = 68 sts rem.
I interpret this as cast off 2 sts at each end of rows 1 and 3. Then cast off 1 st each end of rows 5, 7, 9 and 11. Is this correct?
It sounds right to me. Before you begin the cast offs, do you have 84 stitches on the needle?
Yes, that’s right. Remember too, that since you can’t cast off at the end of the row, you’ll need to turn and do the cast off at the left edge on the next row. Do the cast offs at the beginning of a row. The slight stagger in the cast offs won’t be noticeable.