May I offer one word of advice to our young friends, as someone who has also been booked to 'perform' at a 'session?'

If you feel you're supposed to be doing a sort of gig (and perhaps don't actually know that many well-known tunes anyway), but people are arriving with instruments clearly wanting to join in, all you have to do is explain the situation.

Do some of your own stuff first, then open out the event and let others have a turn, and then perhaps finish with a little set of your own for those who've come to listen to your band.

That way you're fulfilling your contract while still being inclusive.

But actually it's really down to the festival to provide the right information. 'Session' is another word with too many meanings. It needs a phrase to qualify what people should expect - then this sort of thing shouldn't happen.

Tom