It should lay flat, yes. Are you certain that your flat surface is really "flat"; that is, have you tried it on several different surfaces with the same wobble as a result? If so, then you can contact Apple about it and see what they say. I haven't come across anyone with this problem (usually the lid is warped relative to the base), but I would think that for the price of a MBP you could expect to not have to wedge a matchbook under one corner 😉