Notice the shape and roundness of the hips.  You should draw the stripes so that they follow the contours of the hips.  More so, the stripes should also follow the wrinkles of the clothing.  At this point, make the stripes follow the wrinkles that you have sketched rather than force them to follow your subject.  Keep in mind that as the artist, you are in control of the drawing.  Never allow the drawing to control you but use your judgment to force things to look correct if you have to.