Monterey - I feel for you

You were focusing on the mess up - not on a lovely omelette.
Exam/test time sucks. All that passes thru the mind for many is - I'm gonna fail....I won't get thru this. It becomes like a mantra, a self fulfilling prophecy.
Visualisation of succeeding does have its benefits - or thinking of something totally removed from the situation at hand. With practice, it can work. If I have something stressful...my mind goes back to something I deliberately stored in my memories for times I knew were ahead. A memory from where there was no stress, it works for me.
The memory is of sitting on the end of a jetty, supposedly fishing, but just looking out onto the far horizon and letting my mind just go blank apart from the feel of the wind, smell of the sea, sun just gone for the day. I knew I had to store that one.
That was 20 some years ago. Its still clear as crystal.
P.S. The fish weren't biting - doesn't matter

That isn't why I fish