I think I may have screwed up the main Prophecies questline

So, I did the Great Northern Wall mission a while back, I even picked up two pieces of armor by accident.
However, after I escaped from the Charr, I don't remember why, but I fast-traveled directly to Fort Ranik, not realizing at the time that there was a whole questline there.

I can't get back into the area (the path leading down from the wall seems to have disappeared) and the succeeding quest isn't in my quest log for some reason.

Any ideas how to fix this?

Fort Ranik is the next mission. You do not need another quest atm, and the pieces of armor are for the bonus for the 1st mission.

You can go back to the first mission and enter it again do the bonus and once you get rewarded for it you can just leave the instance.

Except I can't get back into the area where the first mission is.
The ramp leading down into the valley area from the wall is gone.

You don't walk through on the map, you need to map travel back to the mission and complete it.
You can't screw up the storyline or questline so don't worry . You just need to figure out what you may have accidentally skipped and go back and do it.

Just hit M to bring up your big map, find the Great Northern Wall mission place and click on it to travel there. You can go back into the mission and do the bonus. Just don't go to the point where the cut scene triggers before you get the bonus done.

Got it, thanks.