Your first open mic will probably be rough. The second one is usually less scary because you survived the first.

What makes a first night terrifying is that the outcome is unknown, so your head is free to invent it. Once you have stood up there, the worst case stops being a prediction and becomes a memory of something survivable. That is the whole trade. A rough first set is not a failure, it is the price of converting an unknown into a known.

Book two dates rather than one, far enough apart to work on it and close enough that you do not lose your nerve. Treat the first as a fee paid toward the second.