Overlock the edges if you choose and hem the skirt and you're done.
Step 12: Sew the band to the skirt
I use my overlocker for this step, but when I don't have an overlocker available I use a zig zag stitch on a regular sewing machine. With the stretch t-shirt fabric on top and the skirt fabric on the bottom stretch the t-shirt fabric from one pin/seam to the other so it matches up evenly with the skirt fabric, then sew in place. Remove the pins and repeat with the other side. When you have sewn the band on the finished skirt will have a slight gather where the skirt meets the band - this will disappear when the skirt is on the body and the band is stretched over the hips/waist.