when I'm making aliens, I just make sure the cores are straight, lay them side by side, hot glue one end, run my fingers down to the other end, and hot glue that end. not much tension on the alien wrap, so they stay flat. on other coils, I do the same thing, but use paperclips, small clothes pins, or a toggle thing from a hoodie to keep them flat. in all cases, you may occasionally need to use a pair of nylon tip pliers to squeeze them now and again.
Sent from my SM-G955U using Tapatalk
edit: as soon as you see your cores start to collapse, stop and fix it. (squeeze with the pliers)