I may be a little nit-picky but let's just see how this goes....
The absolute first thing I noticed was your trot. IMO I feel that you arms are a tad bit too straight. If you just brought your elbows back a tinge, to where they are right at your hips they would look great!
Next thing, I agree with the above that your leaning foward at the canter too much. Sit back a little and get your butt in the saddle it will help with you collection. Also, I see what you mean about your hands being too low at the canter, so again, get your elbows right by your hips and raise your hands up a little, this will help ensure that your hands don't sink into the horse's mane :) Remember there should be a straight line from your shoulder hip(where you elbow should be) and heel.
I agree with Alexis that your first jump approach wasn't great. It was way too sharp of a turn, I think that's why your horse lacked impulsion to the jump. With such a sharp turn he/she had to break down to a trot to make the turn. (This is rather irrelevant but flexibility could be another reason he/she broke down to a trot. With the sharp turn he/she might not have very good bend in his/her neck to make the turn. Ground exercises can help with this, plus suppling exercises,serpentines,figure 8's,front and hind end yielding. Lots of exercises can help with flexibility:))
The second jump was much better. I won't add too much with this one. Same thing as before with the canter, hands, and arms. Also, I think it was better because right before the jump it looked as if she was almost going to break down to a trot, but I think you pushed her foward just enough to keep the canter and for the horse to make the jump.
With the third fence, I don't really think the approach was bad, it was fine. I just think that you didn't really push her/him enough, again, not enough impulsion, thus why she/he trotted down. I think another reason he/she might have trotted down(besides the flexibility) is that with each jump, your strides were very short and choppy. Thus why she either had to trot down or do many little canter strides to make the jump. I think if you judged your distances better she would have taken off for the jumps at a better place.:)
I do like your heel. It isn't flopping around or wiggling a lot(which is one of my biggest pet peeves so trust me if you were, I would tell you). Your lower leg is pretty stable.
Hope this helped. If any other questions please ask and I will happily answer. Happy Riding!!