K, first of all, nice squats, you're taking them deep and that's man. Second, you know somethings wrong and you're asking for help to get better, that's also man.
I found it very difficult to see your body during your squats as the plates were in the way, maybe try getting one a bit behind you and at a 45' angle from the front.
What i'm going to say right away is do this warm up
also do this warm up
the second one will help out with your upper body a bit as you're tight in all the wrong spots.
Also, get weightlifting shoes immeidiately, these will help more than anything else right now.
I'd also add in front squats as often as you can, they'll teach you the proper posture of squatting, you either do them correctly or the bar falls off your shoulders.
Also, when you went for your max, you paused a bit in the hole, learn to stay tight and really "bounce" out of the hole, I say bounce, but it's just the rebound of going below parallel and stretching your quads. The above poster was right on the money about having to stay tight, so try to pay attention.
Overall, your execution of the lift was very good, just loosen up the right areas, get better shoes, learn to love the front squat and learn to "bounce" in the hole. Also if someone tells you to box squat, don't pay attention. just front squat and back squat, you need the reps to learn the movement.