If you are doing clothes alterations for a living and charging for this service, then you really should be doing the alteration as professionally as possible. Some people do not have an overlocker. If that is the case, I do recommend you consider using lace or tape on the raw edge rather than using your zig zag stitch.
It may seem over the top to some people, but again if you are charging then the zig zag stitch is not for the raw edge. The zig zag stitch is for sewing garments like swimmers when sewing on the elastic.
shorten school uniform with pleats
Even a stretch fabric should not really have a zig zag stitch. It's fairly simple to work out. Check out the clothes hanging in dress shops and see if the inside of them is sewn this way.
My policy has always been to return the garment to the client in a professional manner, and I want it to look as good as or better than it came to me. Not the other way around.
shorten pleated skirt
In this video I show you my technique for putting a 7.5 cm (3 in) hem on a girls school uniform plus how I go about lining the pleats so they are even.
Happy altering
Judith Turner