I exchanged my first iPad Air due to yellowing on the left side of the screen. Got my replacement and immediately noticed a chip in the chamfered edge near the top of the screen. Not terribly bad but it's become the first thing I look for in a new or replacement device after going several rounds with scratched up iPhone 5. Ultimately though the screen on this unit was night and day better than the first iPad Air I had. Given all the things I had read about people getting screens with yellowing or uneven backlighting, I decided I could easily live with one small nick rather than risk getting another replacement with a worse screen.
If it really bothers you, by all means return it. But I would think twice about it if your unit has a good screen that you are happy with. There are definitely some less-than-great iPad Air screens out there.