Photos help but if your talking about some color squishing out the seam then just remove it with acetone or alcohol. I have never seen ultra separate as I'm seeing it in my minds eye. Are you overlapping the covering so it's being glued onto the other side or is it slipping off the wood as you shrink?
Your just covering the wing tips? You iron it down with an overlap then ironing it down to the outer wing tip wood then with your iron shrinking the covering? Covering sticks to covering the best, once they touch they are there until you pull it off. I just don't understand what problem your having.