Lee,
Dont worry about that mate! Like you said it has happened to most of us during training. You will find that you learn a hell of a lot more by making a these mistakes. I know I certainly have. I think one of the best things that I have learnt is being able to anticipate the actions that you will have to carry out and try and organise your workload so your not doing to many things at once.
Most people who have done nav would agree that it is the most demanding aspect of the training but it is also, in my view, the most rewarding.
Good luck on wednesday!
Neil