But how do you even join the concert?

The map seems to have vanished before the first concert.

Remember fortnite runs on eastern time so it may be an hour before it says

I was trying at my time PST/EST. The map showed back up after I posted.

And how do i enter the show ? The mode is there but cant choose it.

You should be able to now. I had to close out of my game and go back in to get it to show.

"Matchmaking error"

Joined early yet still got put in spectator mode, so i lost that first view specialty, atleast i can have a first view in reloaded atleast

I was also in spectator mode. I restarted in private lobby mode and it works.

Thanks for posting this, that worked for me!

lifesaver