If you,re leaving them on you will have to clip them as Kad says. I don't make curtains if I can help it now. But when I have I always take the selvedges off. The selvedge is much tighter than the rest of the fabric. So when they are made, although the they look fine to start with, they never hang right. I'm sure lots of made curtains have the selvedges left on. In my experience, many of the are not well made. Including the ones I had done in John Lewis. I also never use selvedges in my dressmaking for the same reason. You always get a distorted seam.