That’s really tricky for you, I’m sorry. Sadly I don’t think you really have any choice but to stay and do the paper. Although sometimes they do cost money, name changes for flights are usually possible. Would your parents have a friend who could take your place? It’s really not nice to have to miss a holiday for the sake of an exam, but when it’s a question of your future you have to put yourself and your long-term prospects first. Depending on the length and cost of flights could you also get a different, later flight? Sometimes time changes are also allowed.