Looks like someone needs a lesson in humility and practicality.
You can't just step into an advanced training seminar, no matter how good of an athlete you are.
For one thing, your body isn't ready to handle the rigors of such a training method. Even if you're athletic, you might not have the right level of athleticism to step into such a workout. Furthermore, it takes time to develop the right kind of conditioning. The class you attended was for an advanced group, who has had the proper conditioning.
Second, you do not have the fundamentals needed to train at a high level just yet. It's no different than a white belt who asks me to teach him kata Unsu (one of the most difficult in the Shotokan system), and he gets frustrated when his stances are wobbly, and that he falls flat on his face when trying to execute the vaunted 540 degree manuver at the end.
The coach was entirely in the right, for telling you to better prepare yourself the next time around. Once you have accumulated significant martial arts experience in a respectable system, under a good instructor, then you may find yourself ready to handle the rigors.
I'm going to be even blunter than the others here. Your situation reminds me of the movie "Star Wars: The Empire Strikes Back."
In a nutshell, you should think of yourself as Luke Skywalker, who only had a very short time of training, even though he had superior talent. After getting your hand chopped off by the highly skilled and practiced Darth Vader in a one-sided lightsaber duel, you had to retreat.
Now, what you do after having retreated is going to shape how you'll develop. If you choose to be patient, train hard in the arts, do some studying, then the next time around, you may very well end up beating the Dark Lord of the Sith. You're going to have to face the music first, though, and in my best Master Yoda impersonation:
"No. Unfortunate that you rushed to face him… that incomplete was your training. Not ready for the burden were you."
Again, think of this as a test for you. If you train first, and then ready yourself for the next time around, I honestly believe that the coach will be very impressed with you, that you had the fortitude to overcome your previous obstacles, and became a stronger person as a result.