Any info might help! Thanks!
Not sure if FT back to Skyrim is possible in that quest and IF you can, there is no way to go back to Skuldafn. Best suggestion is to change the difficulty to novice and just run your way through the place as fast as you can (although I do know will have 1, possibly 2, enemy(ies) that stand in your way; at that point attack/dodge to your best of abilities to eliminate the "roadblock(s)").
Or go back to a save from before trapping Odahviing and toughen your character up before going there. Your choice, lower the difficulty or hold off on it for a while.
This is my advice too. I have done this before in similar situations.
Give it all you've got. Hide, and take all the cheap shots you can. Use every potion in your inventory. And emerge victorious.
And if you die in glorious battle, you will not go to Sovngarde.
Surrender yourself to Nahkriin, and he will put you on the path towards Alduin's forgiveness and redemption.
Do what I did when I got to Skuldafn unprepared: run like hell through the exterior and enter the temple without confronting any of them. The enemies inside the temple will likely not be too hard because they're levelled. Then when you get on to the roof, again run past everything (or fus ro dah them off the side) - if you're fast enough, you can get to the portal before Nahkriin has time to grab the staff and close it, forcing you to battle him.
You do not have to fight the two dragons up the top unless you attack them first, they should just sit there happily watching you, so long as you leave them alone. But still I would go back to a previous save and level up a bit more, it might not be too much fun trying to get through the portal without dying a lot. You want to face the challenge, do a lot of sneaking and use a bow if your character is any good at archery, especially outside it will give you more room to RUN!