POOL LINER POPPING OFF J-CHANNEL

[MATT 1280]

I MOVED A POOL FROM ANOTHER HOUSE TO MINE AND WE LEVELED IT AND SET IT UP. WHEN WE PUT THE NEW J-CHANNEL STYLE LINER IN GOT THE WRINKLES OUT AND FILLED IT WITH WATER THE LINER POPPED OFF THE TRACK. WE ONLY GOT IT FILLED UP ABOUT 1/3 OF THE WAY UP THE SIDES. WE HAVE TRIED IT TWICE AND IT POPPED OFF BOTH TIMES.

WHAT AM I DOING WRONG ????