If those boots are so tight it hurts return them while you can. Boots should be snug tight but not painful. If they are that tight in the shop then chances are they will be hurting you after an hour on the slopes. I went a half size bigger and my toes barely touch the front of the liner (Rulers). Using the same shoe size was too tight, toes were pressing against the liner too much and the top of my foot/toes was starting to hurt. Wear them around the house before you use them on the mountain, walk around and make sure you can stand to wear them for a prolonged period of time.
My Rulers really havent stretched much, they were a comfortable snug when first bought and still are.
Always, always, always, wear the boots for awhile before buying, sometimes "hot spots" (aka pressure points) might not be noticable at first but may arise later on the hill, and always wear the socks at the shop that you ride in on the mountain. I always give my self at least 15 minutes in them at the shop.