I wouldn't worry about the muriatic acid at this point--the high chlorine levels will give you falsely high pH readings, so you'll have no way to know when you've lowered it too much. Having it higher won't hurt anything, but getting it too low will ruin your liner. Leave the pH alone, and keep the chlorine around 20. You'll have to go a good bit above that to do any damage to your pool, so even if it is way high right now, any damage that was done would already be showing itself.

Janet