Thanks for the fast reply, Madjack and rbeemer. Home Depot sells PL all over the store. I don't have any on hand but I have Gorilla glue. So the Gorilla Glue is your weapon of choice when you build professionally?
I don't have clamps wide enough to push in on the walls since it's 76" wide. If I drive my exterior screws nice and tight, should that be enough???? My walls are square as can be without the spars in place. I am starting to stress again....
Madjack, Can I bring it to you to finish before I go nuts

Just kidding of coarse. As long as I have you guys giving me advice, I know I can do this!!!