You probably need to drain it again, leaving maybe 4" in the bottom, and work the liner around to reposition it and create some slack at those points. However, if the liner is a couple of years old this may not work, and you'll have to replace the liner.
Next time, you probably want to avoid draining it completely.
It's not the best example, but you can get an idea from this YouTube
http://www.youtube.com/watch?v=8IALYGRw8lg
AND some of the comments.
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