Bless your heart! If the shop owner was so perfect, why didn't SHE teach the class? Your quilting must be impressive enough if she asked you to teach. I would say she bears part of the blame if she didn't give you suggestions (Do you have guidelines for what to bring to class? Do you have a handout in case someone falls behind, & needs to finish at home? Do you have contact information if someone needs to get in touch with you?etc.)
Of course, these are only things you find out AFTER you teach & falter.Don't let someone else's criteria determine your path.
My job was so stressful that I turned to quilting as an outlet/hobby/avocation. When asked why I would pursue something that required "SO MANY DECISIONS?", my response was that no one would ever be hurt by my choices in quilting. It's not critical -it's a personal expression of creativity. As long as it satisfies that need in me, then it's a success.
And, each person has his/her own reason for each quilt.
Enjoy yourself & let the criticism roll off your back. It's not brain surgery & it's cheaper than therapy!