How on earth is AA going to know that you're OWS if you don't put in your MPC Gold number?
If you don't put down your CX Gold number on your reservation, you're just a basic member as far as AA goes. And if you chose preferred seating, then you are liable to be charged for sitting there.
Why don't you just put your CX number in the reservation and change it at the gate before you board. Then you get all the privileges accorded to being a OWS member including lounge access.