Oh, I have a feeling you will do fine! 
I've done live sales presentations before and it's a similar situation. You feel like you have all the eyes of the world on you. It's not a comfortable feeling. The key is to pick ONE person who has a friendly face and focus on them.
In those moments, when you feel self conscious, look at the child and see how you can help her.
That will focus your attention away from the others and onto a third party who really needs your attention.
Most likely, you felt so confident with your first toddler group, when you ran it, cause you knew that you
could help others and you had the power to effect change. When you are first going into a situation, you
might not have that power.
This might sound silly, but another trick is to keep a small hand mirror in your purse and when you feel out of place, take a quick peek to see a familiar face. Most people can't feel nervous anymore when they catch their own reflection. It's just basic biology. That will help put you instantly at ease until you find your footing in the new situation.
Another tip, just give it time. Situations always warm up as time goes along.
Best of luck.
Let us know how it works out.
