Stephan, welcome to TFP!!
If it's an overlap liner, you
might be able to do it. I would recommend returning the too small liner and getting one that's the right size!
If you have no choice and want to use the liner you have, I'd build up the cove at the bottom of the wall - and hope for the best
Getting the liner ~perfectly centered will give you the best chance of being able to use it (overlap liners usually have 6 -8" of overlap, but an inch or 2 is fine - make sure the 'extra' over the wall is even all around before adding any water - and expect that you may have to drain the water and reposition the liner if any part of it stops being over the wall