I am looking at the Exped Duo sleeping mat as 52 inches wide and it being just as wide as the tent Nemo Aurora 2p. It this likely to cause any strange problems?
You may have problems getting it in and spread properly.
You may find it is just that bit wider it forces the edges of the tent out.
And you may have to put anything you bring into the tent onto the mat, depending on the length of it.
In the past I have used a matras style airbed that fitted snugly in the inner tent I used back then but the tent had a good fly sheet that was enough wider that it did not become a problem. I have been in a tent where any stress on the inner tent would have resulted in leaks through touching layers. In such a tent I would not use a snugly fitting mat or airbed.