Ok, I read in some other question asked that you can go back to Skuldafn playing Skyrim on PC by writing something in the console, but I play Skyrim on my PS3 console.
I need to go back because a draugr thu 'umed my arse into the portal before I was able to kill Nahkriin and take his mask. Can I do it, or am I screwed? Am I now not able able to unlock that other mask in Labyrinthian?
You are screwed. Sorry. There's no way to go back there if you don't have access to the console, unless you've got a save from before entering the portal.
Currently there is no way to return to Skuldafn (not even through exploits, as Skuldafn cannot be found in the "normal" world and is only accessible through that one quest) once you leave. If you missed something, you will sadly have to reload an earlier save.
The chance that this will be "corrected" in a patch is slim to none considering this is not a bug and, aside from that mask, there are no "unique" items in Skuldafn which cannot be obtained some other way (or for which there is no equivalent you can find/craft), so don't count on it.
My suggestion is to find the latest save you have before entering Sovngarde and reloading.
