My brother had no end of trouble with his M7. Sharp edges and not sitting flush. I think he sent 2 back before he just gave up and settled. Again, I was lucky as mine was pretty much perfect.
You should still be able to return the phone shouldn't you? It has a slight manufacturing defect after all. I wouldn't be surprised if they just swapped it for you in the shop for a new one which doesn't suffer with this problem.
I might just pop in to town after work tomorrow and try a bit of gentle complaining, I suppose all they can say is sorry no.