I don't notice any warping whatsoever...
For your case, you can send it back. To me, it seems perfect (or maybe a hair off? maybe I'm imaging it) but if it really bothers you that much, just give it a try.
But I personally wouldn't send it back, for all the trouble in fixing such a tiny problem. As for those of you saying that you should have a perfect machine for the amount you pay for a MBP... you don't. If Apple created every MBP to be flawless - no moos, no whines, no overheating, no warping, no dead/stuck pixels, absolutely no problem imaginable - then get ready to pony $5000 for your machine. Apple gets by because some people don't care about a single dead pixel, a tiny amount of warping, or a dead pixel in the corner.
Just some people (like the OP) are more 'attuned' to certain defects, and what seems like splitting hairs to me might be a dealbreaker for him.