Don't worry, there will be lots of people there who are not Catholic. During Communion it is OK not to kneel if you are not Catholic. Some people can't kneel for medical reasons even if they are Catholic. If you get stuck in the middle of a pew, just move out with the group and stand at the end of the pew until everyone exits, so you won't get stepped on, then just slide back in. People will figure it out when they get back. Or you can go to the end of the pew they are coming back to and just stand there until whoever you were sitting next to comes back.
Catholic Confirmations border on chaos, because of the crowd that shows up. Most important thing! No one is watching you, they are all on their own trip so don't worry about it. No one will likely know that you are not Catholic and they won't care.