Some things, you simply can't put a very narrow hem in... better to put in a facing, turn it back and hem that. It actually makes a cute design element to use a different fabric (calico print for jeans) to face it with. You get an occasional glimpse, depending on length and tightness of skirt... cute!
On my jean skirts that do that, I actually take them and put them on a hanger, moisten the hem and just pull and flatten it down. If it is real stubborn I will fold it backwards and crease it with my fingers. Sometimes it seems I have to do it every time I wash the skirt, but it helps. (ironing does too)