Mike, it's ok to fill the pool before installing the faceplates and cutting out the liner. In some cases the water has to be up to prevent wrinkles, especially when an inlet/ outlet is located close to a corner that hasn't 'fully seated itself'. Don't worry about it, he's the one getting wet. Congrats on the pool being almost finished, with luck you'll be able to enjoy it a couple of times before you have to close it