Wow, I thought I was just being shy, but I've been adhering to a similar strategy my whole life when joining a new group: stay back, let the group welcome you in instead of forcing yourself into the group. I also find that befriending single members of the group outside of the normal group environment works well in gaining some legitimacy in the group. After friending one person, you just apply the transitive property of friendship a couple time and hey! you've got a ton of new friends.