okay, so first of all, you can always back out if you dont feel up to it? No ones gonna force you to go if you dont want to.
But going to a different country for a concert is very good life experience and its impressive to have that on your CV and Personal Statement if you want to apply for uni in the future.
Maybe you can try to sort of 'practice' being away from home for a bit before the trip? If you have any close relatives or friends, you could ask to stay over at theirs on weekends to get used to being in a different environment.
Or you can try some different herbal remedies for anxiety. Theres different calming teas (like camomile tea) and natural medicines you can get at Holland and barrets. Sometimes just the scent of lavender helps, you can get sprays to put it on your clothes to calm you down through the day?