I don't know what Apple's new purchase customer satisfaction policy is in Northern Ireland, but it's really up to you to decide whether or not you want to live with it as it is not functional damage.
Since you didn't bother to attach a photo, there's no way for any of us here to assess the ding.
Personally, I'd probably try to get them to replace it. I tend to keep my Macs for many years, so I'd might as well start with something pristine. But that's just me...