The Fearful Instructor

I had just completed a Pilates Teacher Training. For a long time I thought I would make an amazing instructor.
During the course I got ongoing feedback from the teacher about my cues for the students and that I need to make them clearer and earlier.
She kept pointing me out and following by saying ‘That’s how you Don’t do it.’
Upon completing the course, to my amazement I was offered a job as an instructor in that studio.
Yesterday was my first class and I studied the sequence of exercises by heart and practiced it at home.
Class started and I blackout and forgot everything. With a full hour ahead I managed to pile up enough exercises and complete the hour with everyone alive.
Then I walked into the management office and resigned.

Looking back I can see that I had a pre-class model:

C: First class teaching
T: I hope I will remember everything
F: Afraid
A: Prepare thoroughly ahead of time
R: I blackout and forgot it all

So something doesn’t make sense to me in this model. If I prepared so well why was I ‘rewarded’ with a blackout?