I've literally joined up as mine is exactly the same as this. I don't know whether to return it or if I'll be laughed out of the store and part of me is thinking the bend is just amplified in my head as I spent £700+ on the device and now I'm paranoid it's not perfect.
If it bothers you (and it did me) then I would take it back - when I took mine back they just asked what was the problem and checked there was an iPad in the box, but didn't inspect its somewhat curved nature. I am beginning to think that most/all have a slight curve but it bothers people to a greater or lesser extent (or some don't notice). On my replacement you really have to look straight down the edges to see any curves to the point where I believe it is as good as it gets and I have now forgotten about it.