Pigtails, it sounds to me like you're second-guessing everything. For example, your input about being the sibling of adopted children could have been interesting and helpful to someone who is thinking about adopting.
I think you will become more comfortable in your skin as time goes by.
That said, I no longer enjoy being in groups like that, where I am not quite close with at least some of the people. I used to do that, for many years actually, and I never liked it, so now I say 'No, thanks' and do something I'd rather do. It could be that you just don't connect with any of the women and the group doesn't work for you.