I'm at the end of Mourning's End Part Two and I'm at the part where you need a death talisman to enter the altar, right?

So after the cutscene with the dwarf, I teleported out to go get my death tali and when I come back I can't go through the light door between the double stairs..?!

 

What did I do wrong?

Sounds like you did not rotate the mirror back to be able to pass through the cyan door. There is a back door you will need to use that is in the underground pass area with the dwarves to get back to the alter area.

Yea, I figured that out now =[ Anyway I just re-did the sixth door so problem solved :D