The anxiety is caused by the fear of being responsible for the outcome, and trying to get away from that fear but unable to due to the nature of the affair.
Moment like this is a golden opportunity to train to muster some courage, since life's journey ahead is long. Stand your ground and be counted. Be willing to shoulder whatever that is coming your way.
Children's anxiety usually reflects that of parents. So, be a real parent, and share some of that burden by telling the child you will be happy with any outcome, because you all did your best, and no one can ask for more.