SPOILER!

I started the quest ok, and fought Alduid until he left. Then I spoke to the Jarl about using his castle to catch the dragon. I also spoke to the graybeards about the truce, then I TRIED to speak to General Tullis but all he wants to talk about is me joining the leagon.

Where did I go wrong?

I think you may have to join a faction (either Imperials or Stormcloaks) to continue.

You don't need to join a side. That's what Season Unending was meant for. Those who haven't started the CW and those that haven't finished the CW.

He dont have to ive done it without joining any

They should be a speech option if not try talking to ulfric first an if not then if you got a load before you started the fight then id suggest you load an try it again