Terrified about my first meeting with students tomorrow

Hi all, I'm a student teacher, with zero school training or experience, but due to lack of teachers, a bunch of student teachers in my area have been put into classrooms all over the county. Long story short, I'm the only teacher for a classroom tomorrow, finishing out the school year with kids who had their teacher quit in March. I have 5 classes of 5th graders, and I have no experience how to run a classroom. I'm prepared to fall on my face, but I don't know how to get back up. I'm a high school English student teacher, not a trained elementary school teacher. I'm meeting with a school principal from another school this afternoon to help him set up the classroom and lay out the curriculum, but I'm really freaking out. I will probably put my email in my profile if any of you want to give me advice.