I've installed a few headsets with your method without washers inside the cup and I've never bent the cup walls. They are very strong.

Stuff, like that lower retainer ring, shouldn't be moving around. Try putting it all together and see where that gets you - it may just disappear. And if and when you put it together and it the are "feels" right, as in correct preload with no play, then it is likely that it is like that.