The best way to keep it from shrinking is to wash on cold and line dry it. I have also found they shrink up a bit in the wash. So I have my dh or my dd pull each end when wet. Pulling help stretch it back out and I also found that way I don't even loose an inch. Didymos says they are made long to shrink a few inches. Just don't put them in the dryer. The fun part is trying to find a place to dry it inside.
Beth