There is something not quite clear to me about the placement of the markers. I can't picture it in my head and I don't want to tell you the wrong thing.
I understand that the pattern want you to cast off at each end of every other row.
You do 7 sts cast off at each end of every other row for 8 times. Then do 8 sts cast off on the last one.
is it possible you could show me the pattern or send me a link or something? That way I can see it better.