I inserted four grommets in regular distances. The fifth will be added afterwards. I ironed the lower curve inside - now there are three sides sewed and one's waiting to be.
I took four rectangles of canvas, pleated them and pinned into each piece. The fact that I'd ironed both layers assured me that I'd hit them both when sewing.
I sewed it and placed the fifth grommets. I hope I'll have my real skirt a lot wider...