I can't believe the people suggesting not returning it, comments on the people stated otherwise (out of principle, wrong). We are just giving opinions.
A scratch on the case does nothing at all. I might not even bother to return/exchamge.
But a scratch on the screen (glass) is another story, especially the thread starter used "hairline" to describe it.
There's a possibility that it might be a hairline "crack" (The thinner it is, the worse it is in my experience). A piece of glass is durable until a crack is formed. Every time a lid is opened or closed, keyboard contacts, temperature changes, will give pressure. It will grow over time.
How do you tell between a crack and a scratch?