The water under the liner is probably what helped push the rest of the liner out of the track - you've got drainage issues with your yard.

With the liner floating, it might be easier to get it back into the track (see the sticky in Pool Construction and Repair).

I'm more than happy to help with your issue(s) but it's really busy at work right now, so it may take me a couple days (and a "bump" from Watermom )