You came out of a save, and any load-trigger (door, savewarp, respawn etc) will take you away from Layer 8. That's why normal FF2 happened

Which dark FF are you talking about actually? The one where you go to the door at top or the one where you get the Gossip Stone?

If it's after the Gossip Stone, you need to go back and get caught again in the same sub, then go to the top of FF, go in, respawn and you'll be put in Layer 8. From here, don't trigger any loads as mentioned before, and you should be in the correct layer 8.

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Edit: I'm mostly getting this from the Route as mentioned in the video by Gymnast.