How do I get into chamber choir?

For now I would approach somebody you know who is in a chamber choir, or else find out who leads the local chamber choir and talk to them. Ask their advice on how to take the next steps in improving and ask if they can help you practice.

Being frightened when singing in front of lots of people will happen to everyone so ask everyone else how they deal with theirs and just make sure you practice lots. Practice in front of friends and family and in your room and just make sure you know what you are doing as it will help you feel more confident. Remember that there are lots of you together when you are out there so no one is focussing on you and just try and take deep breaths and concentrate on just performing. Forget there is an audience there if you can and just imagine you are there with just your friends and family. You will soon get over the stage fright after you ahve performed a couple of times :)