You can take it to the Apple store to get it looked at. But even if it is an obvious flaw they will often say that it is "within acceptable tolerance" and throw you out.
If they are in a good mood they might replace your unit. However, if you are unlucky, you will open the box and discover the second one has a bigger gap than the first or that it has a different and even worse defect.
This is just the state of Apple hardware quality and customer service nowadays. Nevertheless, if the gap really bothers you, you should probably give it a try and see if you can get a replacement.