I'm in the exact same situation as you. I was on the checkout screen yesterday and thought I'd better call them. So I called and said, "I'm about to preorder a Galaxy S8+ online. It says it will be available for pickup on 4/21. Is that guaranteed?" She said, "If it's letting you preorder, it means we'll have it. Let's say you picked black but we only had silver, it would say Sold Out if you selected black. If you can order it, it'll be here." I felt a little better, but I won't lose this butterflies-in-the-stomach feeling of uneasiness until I'm walking out of the store with my new Black Beauty in-hand.