So now the waistline is too small? If you only need to increase size by a small amount, you can decrease the seam allowance. So let’s say you stitched a 5/8″ seam allowance on each side seam. If you were to go back and make this 1/4″ seam allowance instead, that’s a difference of 3/8″. You would multiply this by 4 since you have 2 front sides and 2 back sides and you’re giving yourself an additional 1 1/2″ total to that circumference. Need a little more? You can also decrease the zipper seam. Yeah, it’s a pain in the neck to take out stitches and redo them but it’s a quick fix without having to remake the whole skirt and do a pattern adjustment. Hope that helps.