i'm a new pianist too, but i got a few suggestion of mine which i think it works.
1.try to reach the exam venue earlier(but not a few hours before it starts)i think this will help one to get familiar with the surroundings and make u feel more confident and comfortable,also try to walk around at the waiting room if u can
2.if ur teacher is with u at the waiting room, try to ask some question about your pieces or scales etc.maybe this can helps to help u to relax and also helps u lose the nervousness that u'll play the song wrongly
3.lastly.of my own opinion, i think u should laugh a lot when your're waiting and talk a lot too.if u just keep quite sitting there,waiting...it'll just give u a more nervous effect.coz if it's so quite , it seems that it such a formal and strict exam and .........(u should know the effect)
that's all , hope this will help u.andi'm curious that why r u still nervous?since ur already a grade 7 candidate.didn't u have tons of experiences??still nervous??

have a smile and every thing will be going on smoothly.