@MRSHINYSHOES said some very good things. The worry is always worse than the reality. So the question becomes how to get rid of the worry.
There are many ways to do this. I use a breathing technique my therapist taught me to help get rid of anxiety. I hold one nostril shut while I breathe in through the open nostril, and then I slowly breathe out through my mouth and use my diaphragm to push out as much air from my lungs as possible. This helps relax your muscles and releases anxiety.
Exercise is another effective method of reducing stress. If you can, go for a brisk walk. Just walking twenty minutes three times a week will make a tremendous difference.
Clean something. I’m serious. Wash some dishes. Dust a room. Pick up and sort laundry. I know it sounds silly, but I do it, and it works. It takes my mind off the thing that is scaring it, and it puts my mind on something that I can accomplish.
Finally, remember that when you get to high school, you don’t have to have all the answers. It’s okay to ask for directions. It’s okay not to be the smartest kid in the room. It’s okay not to understand everything the teacher is talking about. You are there to learn, and you can do that if you keep yourself open and teachable.
Enjoy!