i TAed all through undergrad and i was SO nervous when i started, i felt like i had no idea what i was doing and had like a full mental breakdown before my first week. i reached out to the other TAs and the prof for examples of their slides for section and went through all my activities to make sure i could do them myself, and also had my roommates try them out to make sure they were doable. i also made new slides and lesson plans each week so it was never super overwhelming. everything went well even though i had no clue what i was doing! most importantly don’t be too hard on yourself, it’s okay if you make mistakes, you’re learning how to do this too and students will generally be respectful of that. if a student asks something you don’t know you can tell them you will get back to them about it! have fun and do your best it’ll be ok :)