i know exactly how you feel but believe me, it gets better.
Since you have an adult class. try to relax and start by explaining the basics of the language. I usually introduce myself,refer to my age and experience and I sometimes answer to questions about myself. Don't get carried away! They need to understand that you are confident.
Ask a few things about each person in your calss. And start the lesson.
Be polite but firm. Have patience and set your rules by presenting them as the best way to understand eachother.
Explain that Hw is essential and begin by expecting from each one only the best they can do.