Nervous about upper level class discussion section

I'm a freshman taking a 400 level history class because I was very interested in the topic. When I emailed the professor, she encouraged me to register for the class. So far, I've been loving the class, but I'm nervous for my discussion section. Almost everyone in the class is a junior or senior, and after reading the graduate student's expectations for discussion, I'm scared I won't be able to contribute meaningfully. Speaking in seminars/discussions makes me anxious no matter what, and some of the readings have been somewhat challenging. I can understand them, but I don't know if I can have a meaningful conversation about them. Also, many of the students already seem to have a solid understanding of the subject matter, despite the fact that the course assumes no prior knowledge. I'm scared that I'm just not smart enough to take the class. I'm hesitant to talk to my professor or the graduate student leading my section because I don't want them to suggest dropping the course. Any advice/encouragement?

Also would it be rude to talk to my professor about my concerns before my section's graduate student? My professor is really nice and I've already spoken to her, but I don't know the graduate student at all.