I am a beginner also, but kind of in the same boat as you. I've done a ton of research and talked to several people here and at my barn. Here is my feedback for you:
Your attitude has a big effect on the horse emotionally. I'm guessing based on several posts I've read by you on the forum that you get on the horse very stressed out and nervous. You expect something bad to happen because something always does.
Someone once said somewhere that horses are mirrors of ourselves. You can't expect to get on a horse while you're nervous and have a great lesson, because the horse will pick up on that and figure you must have a great reason for being nervous and therefore it should be nervous too. Then it acts out, you get more nervous, and it escalates to the point where the horse just wants you OFF.
I've been very nervous riding myself, so I know the only solution to not being nervous is to start back from the beginning. Just saying, "I'm not going to be nervous," will not work! Confidence is what gets rid of nerves and you can't have confidence if your skills are lacking.
SOLUTION: Ask your instructor to do easy, easy basic lessons for a while so you can build your confidence back up. That's what I did. It worked really well.
Just a few weeks ago you were posting that you gripped the horse too much with your legs. That means you need to work on your seat, your balance, your cues, basically almost everything. If you can't trot without stirrups and without bouncing, you shouldn't be cantering. It sounds like your instructor has pushed you too hard, too fast, and now you're suffering the fallout.
Riding should be fun. A challenge, but not a death match. Find another instructor, and if you can't, have a heart-to-heart and tell her/him that you need to start fresh and build on your foundation first. This could even mean going to a longe line and learning to ride first without reins and stirrups. I hear there's nothing better for learning balance than that!
And for some inspiration, a video for you from the Spanish riding school in Vienna. Watch these guys do their training on the longe line! The longe line stuff starts in the last minute of video 1 and continues in the beginning of video 2.