Measure from your coping (where the liner actually beads into the track) down to the water level. If it is even all the way around, your liner has just stretched in a bad way and the tile border is just stretched more in some places than others. This is easy to fix.
If the measurement is not even all the way around the pool is off level. This could be very difficult to fix, depending on how far along the PB is.

Brad
www.waterworkspools.com