I just received the MBA 11" Tuesday. It's custom built, and it's beautiful and all...but I think the 13" might be the better option. I know Apple is good for returning items, but here's the issue: that gift card I received with it has been used a bit. If I brought my 11" into an Apple Store, could I simply trade up to the 13" and pay the difference? My worry is that since it's custom built, I would have to ship it back, and since I don't have the gift card, it would be an incomplete order. Thanks in advance!