The first thing that I would do is call Apple and/or go back to the store you were at, be honest and explain the situation, perhaps Apple will help you out, perhaps they won't, but it's not going to hurt to ask. Really, I think they should provide carts at their stores, but I don't think it's their fault that this happened; although, that would most likely have prevented it from happening.
The second option that I would look at is just pluggin in an external monitor, they are really cheap these days.