Firstly, well done for going!!!
I used to be exactly the same as you....infact, one of my reasons for not staying to class was because I hated the thought of having to speak in front of everyone, so I used to just get weighed and go, not really ideal and misses the whole point of the group therapy thing!!
However, there have been groups where I have had a quiet word in the consultants ear and asked her not to read out my losses or include me in the discussion, that meant I could stay to group, learn from others but not have to speak myself!!
Try and use it as a confidence builder. Try to think of it as being amongst like minded people who are all striving for the same thing (weight loss, however much or little) and remember that some of them will be just as scared as you!
I have to say, now that I'm older (40!), I don't have a problem with it, I'm not sure if it is an age thing or what, maybe going to all those SW groups over the years has built up my confidence? Who knows!
Good Luck to you and well done again!!!