In labarynthian (may be spelt wrong) there's the place that when you put on the wooden mask, you travel too and you collect all of the masks to put on the shrine. I have collected all of them but Nahkriin's mask, as I did the quest quite early in the game I didn't take the mask of his body because I didn't know the importance of it. Is there any way to retrieve it?

And by the way I am on play station so I cannot use console commands.

Im sorry, but youll have to save that for your next character.
There is no way to retrieve it.

Ouch... That's why people don't do the main quest immediately

aaaaaahhhhh I was worried people would say that, and I cant really start again because im nearing level 50. :/

Given how OCD I am with all my characters about collecting rare/unique loot, I am surprised that you didn't grab the mask.

I made the same mistake.