I would guess the WORST you did was fade it a little. It's not good to go that high, or keep it there, but I expect you'd have more damage letting pH go too low.

I wouldn't worry if I were you. Eventually, you'll have to replace the liner. It may be 5 years, it may be 15 years. So, until you actually have problems with the liner, there is NOTHING you can do, so why worry? Go swimming instead!