Neatening/finishing raw edges
An over-lock or serger machine with differential transport (also called differential feed) is ideal because it not only neatens/finishes the raw edges but also prevents them from stretching. Elastic threads are particularly suitable as under-threads (available in well-stocked haberdashers/notion stores). If you do not possess an over-lock (serger) machine, neaten/finish edges with seam or hem allowances with a large zigzag stitch or over-lock stitch, stretching out the edges while catching in an extra thread. This will help you to push back the edges to their original length before ironing them flat. If the edge roll sich inwards, do not zigzag-stitch them right on the raw edge but about ½ cm further in, with an elastic triple zigzag if possible.