I would honestly say still turn up.
When I rang up to check if I was still meant to be attending, even though I hadn't sent my confirmation email, the lady on the phone sounded a bit like, 'yeah of course you're on the list you chose the date so you're obviously meant to be coming'. She didn't say those words obviously..
But I would really try and come. Like whitelighter said, it really won't look good for you if you don't come..
I don't know how many people are at the stage 3 interviews. But I'm guessing it's only a few cos of how long the interveiws are meant to be.
Good luck with your decision making, and hopefully see you tuesday!!