im pretty sure u cant access last carnival in rocco down after u finish the story missions.

Last Carnival is a Level 55+ quest, you won't even enter it once due to the level up rewards going over that

so does that mean its undoable?

It is doable, just unlock it. Even though it is not ran that much

im level 55 atm so do i need a higher level to do it?

57 iirc, yes. Then you will have some quests to unlock them alongside the Advancement

thanks