This skirt used to be a bit longer and look like THIS. I simply chopped some fabric from the top and sewed on a length of elastic as a waistband.
This skirt used to be a DRESS and was just hanging around unworn in my wardrobe. I chopped it in half and made casing from some scrap white fabric to house some elastic. I also put in a small amount of lining just to stop it being so see through. I wear this regularly now it is in skirt form, so don't be afraid to chop up your hard work into something more suitable - what a waste to have things unworn and unloved!