Mine was a little stretched when I got it - the guy who sold it to me on Ebay had used it a few times. Why he didn't like it, I'll never know.
Anyway, I expected it to stretch, so I went ahead and stretched it as much as I could myself. I hung it, tightened the hell out of it, then layed in it for 30 mins - 1 hr. Then get up, retighten, and repeat. Keep going until it stops noticeably stretching. I haven't seen any significant stretch since.
"Physics is the only true science. All else is stamp collecting." - J. J. Thompson