One who is not really sure about ones dogs ability to perform a task in public will become nervous. The answer is of course to train the dog to do much more than the public (spectators/judges/field servants) could possibly ask for. If you know that your dog is capable of much more than anyone can possibly ask for (and this "asking for" is strictly regulated in the field trial rules so you don't have to worry about someone asking the dog to take down the moon for them), then you can relax under even difficult conditions.

The trainer makes me nervous, is so picky that I am so scared of doing it wrong that I am frozen in indecision in case I don’t do it her way!

This may not solve your problem unless you can find a trainer who can help you to go further from where you are now. We use to have a retriever or two in each obedience class and all of their owners say that they can retrieve. When we put down, not throw, a dummy a meter or two in front of the dog and ask the handler to command the dog to bring it to them they without exception, so far, have failed! The dog suddenly do not seem to understand the command at all.

He will always ‘hold’ whatever I ask him to do.  I taught the retrieve “backwards” in reverse chaining, taught him the hold in mouth sitting in front of me and then to come six inches, then to pick it up from the floor still facing me from about 1ft and gradually increased the distance.  
 
My late Springer was once with Maud up in the mountains to hunt grouse. They wingshot an old cock grouse in cover of dwarf birch over some pointing dog and sent it to fecth. It worked and worked and could not find the bird. Then Maud sent Springer. She also worked and worked and after a long search she finally came back with an empty shotgun shell in her mouth! The shell was left by some hunting party the day before and at least there was some human scent on it! Springer might have thought that "if I cant find the bird, maybe this was what they were looking for!" I still get a tear in my eye when I think about this )

She tried her very best for you.  I still get a tear when I see the last photo of Foxy.

along the road. Those handlers who are not constituted that way will however become uncertain and more and more nervous with each failure until they are, like Cj mentions, tensed up enough to affect the dog in a negative way. This results in still another failure and still another nervous breakdown for the handler.

Very true.  Once you get a failure you are more and more afraid of the next failure.

puppy to know if I still am. However once you know your handicap and can adjust the training to it, then you will get a better that average delivery to hand.

How to adjust the training!  Be more calm, laugh more, relax more, obedience training?

Have a good trip, then give up work and really live

Sonia