Is the magnetic strip staight or does it want to curl? If it came off of a roll they sometimes won't stay on well. I haven't done anything but stick them on, But a bit of fabric glue won't come amiss.
I prefer using a flat magnet piece. I like to get the magnets for business cards, It is flat and stays on well. Of course I use cotton. If you are using something other than cotton I don't know how it will work.
Does this help Sheila?
Another thing I like to cut the magnet in a long strip rather than using a small square or circle shape.