Seriously he is going to be fine! Try the out of the crate stuff. Leave the muzzle on for now. Too bad if he wants it off. Leave and go to the corner store or something and honestly when you get back in about 20 mins you will know how he is doing. He more than likely will settle. If he has proved himself in that space of time then leave him many times tomorrow, exercise him, and then go to your event. Worry cause you will, and I bet he will be sound asleep. You are not in over your head. This is still early days for him and he is still learning to be a reliable household member. I know you get sick of hearing it but you need patience and a longer view point. he will be a great pet and it is your job to teach him to be. It takes time especially for the youngsters. You will both get there and yes there will missteps along the way. If you expect that to be so, you will stress less and be thrilled when they don't happen. Good luck.