In Los Angeles, I had ordered on the 12th Pre-Order day (though a few hours after pre-orders opened), and for in-store pickup (which I prefer) for this Fri launch day, only one of the stores (a bit further away from me) had stock of the iPhone Air 256gb Cloud White available. So I ordered it.
I randomly checked again today, and a bunch more stock seems to have opened up, and I could get the same phone still for this Fri launch day in-store pick-up, at a bunch more stores. So I re-ordered it for Fri pick-up at my closest Apple Store (at 9am, perfect time for me!), and I'm going to cancel the other pre-order I made.
So at least for the base Air in this color way, looks like Apple added some more inventory. I would imagine there'll be a bunch for walk-in too like others have said, but check again, maybe your local store got some more stock in to pre-order and guarantee a phone for you?