Sometimes students make the best teachers, because students know that they don't know everything, and they are willing to learn from THEIR students. Now, aside from that, if you are in the role of the teacher, then you have the authority of that role, so play it.

Don't compare your knowledge to the people who are doing this job "professionally" and who know much better than you about anything you want to teach. You'll just feel small and insignificant that way, and you'll sell yourself short, and your students won't get the best experience of YOU. You will pick it up as you go along, so don't worry about it at all.

Focus on what you can bring to the table as compared to the students. They're who you're there for.