I have no idea if you can fix this but if you need to soften and stretch the liner you can spray hot water on it. Some people have used hair dryers but with hot water there is less chance of melting it and you can cover a larger area more evenly. If you can get a garden hose on a hot water tap, that's easiest. Otherwise you can use a garden sprayer or just pour it on somehow.
Hope this helps.
Al