That was great. I enjoyed your performance. Funny thing: your opponent's coach, Todd Medina, was my first jiu jitsu instructor. I also enjoyed the commentary from--if I'm identifying him correctly--that sounds like mma comedian "Renato Laranja." He's a funny guy.
Anyway, on to the technique. Very good for somebody who hasn't been doing this very long. I really like the way you held the back of his neck and hit him when he was down. That was great. I don't see enough mmartists do that. For some reason, a lot of people just stand there swinging and missing with both hands, rather than holding the head in one place and hitting it with the other hand. Awesome job. You did a good job finding opportunities for knees when he would initiate a clinch. When you do those, flex your abs before you throw and really thrust with the hips to spear the knee forward, rather than swinging the upper surface of the knee towards him in an arc. The more thrusting the knee is, the more damaging.
I can see where those head-kicks would have been more on-point if you had more traction. I also like the opportunity you saw in the beginning to throw a snap-kick to the body. I think that helped start the wariness he felt that ultimately enabled you to control the whole flow of the fight.
And I apologize if any of this is old news to you, I know there's often a difference between what we know, and what we're able to demonstrate in a fight, or maybe what an observer is able to pick up on. So, in my opinion, the commentators were right though: your chin is up. There are people who can make a more "traditional martial arts" (ie. karate, kung fu, etc) style work in mma, with the head pulled up and back, but I think it's a better idea to go with the style of head positioning used by the other, full-contact striking sports, that is: boxing, muay thai, etc. in which the chin is more tucked down or behind the shoulder. Trying to make your head far away from the guy at the same time you're trying to punch him by pulling your face back away from him is not what I would consider the best technique.
It looks like you have pretty long arms, so this might work for you for a little while, and against certain people, but eventually, you're going to have to rely more on timing, and getting your head out of the way of any possible return strikes coming at you at the same time as your punch by making sure your head is not in the path of any possible simultaneous strikes--like to the side of the possible strike, rather than being too far away for his punch to reach you. Or, alternately, if both you and your opponent throw a punch at the same time, your chin is more protected at the moment of impact by an obstruction such as your shoulder or hand, or protected by your posture being better to absorb the impact...or his hits your forehead and yours hits his chin--something like that. These are generalizations. In boxing, when you throw a check hook, you're kind of pulling your head out of range of your opponent's strike as you land yours, but that's sort of a different thing.
Boxers obviously try to slip or duck punches, or parry them to the side with their arm or glove, or block them. I'm sure you know that, but what I want to suggest, is that--even before you get to the point where you can matrix out of the way of everyone's punches like old-school Anderson Silva--you try to incorporate more boxing-style defensive movement into your game. That would be my suggestion. More lateral footwork and movement of your body would help your offense, too. There were moments when you had hurt him, and if you had had a little more time up close to him, you might have finished him off. Instead he was able to back or circle away. Using roundhouse kicks to the legs and body can help you corral someone when he is trying to move away.
One more thing. I'm guessing you mostly came to this forum for striking advice, but I've got to say: he did give you that guillotine a few times. I know you're new at this, just make sure you get that down fairly soon. That's just one of those fundamental mma things. You HAVE to know certain things in mma. You have to know how to sprawl. You have to know how to throw a decent punch. You have to know how not to give up position on the ground. And you definitely need a decent guillotine in amateur mma. If you didn't want to throw your hips under him and commit to a dangerous position at this stage in your education as a fighter, with your long arms, you could have at least tried for a prayer choke. Hell, even if you were really enthusiastic about the idea of pounding this guy out with your strikes, you could have used a little grappling leverage to get there--wrap your arm that's headlocking him across to grab the tricep of one the arms he's using to post with. Eric Paulson calls this position "Bakersfield." You can also cup his chin in your hand. When you've got your hand around his upper arm or his chin, you're limiting his ability to move out of the position...you're limiting his ability to move out of the way of your strikes...it's a win-win all around.
Anyways, that's my two cents. You looked good, and I hope you keep doing this as long as you're having fun and it's a positive influence in your life.