A small diagonal cut at each corner stops the raveling and I have had no issues. I would not cut the fabric before, you don't know exactly what measurements after shrinking you will need. I have done 10 years with very little threads getting tangled. I tried sewing down the edges, but too much time, just cut each corner - simple and easy. Good luck.

I no longer have that problem since I started serging the edges. No strings and less frustrating :)