Don't stress. I have been to classes like this before. I used to take classes before my DH passed. There was a teacher that made you feel like you just never quite did it correctly. I remember when I took one class I was astonished when she said my fabric color choices were perfect. I nearly fell off of my chair. I didn't stress, it was just her teaching style and you definitely learned a lot. (It took me days and several stores to find all of the fabrics that would go together.)
When I was teaching classes, I usually had extra supplies just in case. I also gave a supply list that students received when they registered for the classes. Because of the classes I had taken that were pretty high stress, I always made my classes very relaxed.