OK, well first I'd like to say that your horse does have a lovely trot, his walk however, does tend towards being lateral. Whether this is trained or natural it is going to be a large hurdle in the training of this horse.
Another thing that I would like to point out is that in training level, working gaits are shown. The gaits you are doing in this test are not working trot/canter, it's some half jog/lope. These tests are to judge the raw talent of the horse, so you need to show his gaits in a clear, forward rhythm. Your transitions are sloppy and your horse is not accepting the bit, or any of the aids for that matter.
That would be what I see that would justify the mark in the test.
As far as for your riding, I really hope that your coach has you on a schoolmaster in a lunge lesson to correct some of your habits, and I also hope that he is in part time training. He looks like he can be quite a bit of horse.