+1 to the previous comments. The dealer should have adjusted the setup before you walked out the door. I had a dealer adjust a setup for me with no commitment to buying a guitar - I said the action felt high, can you check it while I grab something to eat, and when I got back, it was perfect.
And to give you an idea how a neck can shift, I once bought a guitar that was set up perfectly in the shop. Three hour drive home, put it in the basement. The next day, it was maybe a bit buzzy, but nothing that gave me any cause for concern. The day after that, virtually unplayable.
It's wood. Shift happens.