Thank you both for your comments. You are right that washing didn’t help but I was following the instructions. I’ve never heard of fraycheck - will look it up before I decide which way to go. I’m not too worried about the work involved, I just don’t want to ruin it!
I'm not sure how you are going to finish off the bunting. If you are not binding the edges then I think an overcast stitch would work. Or you could paint the raw edges with watered down pva glue or "fraycheck".
Advice, please - I have just finished some cross stitch bunting, washed each flag as suggested, and am ready to finish off and string the flags (5) together. My concern is that there is already some fraying of the Aida and i’d like to prevent more. I could finish with a blanket/overcasting stitch or would it work if I bonded them to vilene? Or, does anyone have a better idea?