The fabric is so fine and flimsy, that I found it almost impossible to make a nice rolled hem along the bottom curved edge. So I applied Fray Check to that edge, and let it dry. That stiffened the edge, giving it much more 'body', and I was able to pin and hand-sew the hem.
Then I thought maybe an 'armband' of wide elastic might work. I tried making one with a snap closure but it made for a big, unsightly bulge. So I ended up with a simple loop of 1/2" elastic....