LOL Oban got his CGN at 9 months but we had a couple of exasperating class sessions too. I always found a break in training helped, a short holiday. A couple of days to a week where we continued basic manners but otherwise just went out and had fun together.
Will Mia be in the same test? Will the test be in the same place you train? I always thought that would be an advantage but now I'm not so sure. Ours was outside at an all breed dog show and I was just like you, already mentally thinking it would be nothing more than another training class for the real test, a test run if you will. But Oban was overwhelmed by the new sights and sounds and smells and was good. Well, good enough to pass.
Good luck, just do your best.