I think that a little bit of nervousness/anxiety before an event like this is completely normal. I would be intimidated, too. But I think you just need to remember that reading your writing out loud, and performing it in front of an audience, is a huge step and it means you’re willing to take your work to the next level. That passion and that courage will take you far in writing.
When you share your work with others out loud, you’re opening yourself up to them and showing them a little piece of your soul. It’s a very brave thing to do, and I can assure you that your work will always touch someone in the audience. There will always be at least one person who is moved by your writing.
I think you need to remember, when you’re about to go up there to the mic, that there will always be things in life that we are afraid of, things we don’t want to do or do want to do but that scare us. And most of the time, those things turn out better than expected, and in the end, we’re glad we did them. This has happened to me plenty of times, and I’m sure it will happen for you on Thursday.
Just writing the work you’re going to read at the open mic is a huge accomplishment. You should be proud of yourself for that. And you’ve already made the decision to read your work at the open mic. That decision is a huge accomplishment, too. Now you just have to read the work! Two of the hardest steps are already over.
So go up there with a light heart, take a deep breath, and remember that you can do this, and that you’ve made it to this point, so you can make it through the next point. :)
Good luck!