Teaching is difficult.
Yet, like all skills, it gets easier with purposeful practice over time.
Your first lesson is going to suck.
And, because you're your own greatest critic, it will play out in your head far worse than it actually was.
But here's the good news:
That's the worst you're ever going to be.
It's all uphill from then on. With some dips now and then, when you're testing out new material, delivery styles, methods, etc.
So, bite that bullet, make that first foray, rip off that band-aid, and make it your best worst performance.
You'll be much better than you thought you taught.