Wow lots of questions. My instructor has seen me but just kinda stares at me lol and knows not to say anything when I'm pissed. Ummm as far as bit goes I just changed it but I don't know which one it is but it's not twisted and its also a d-ring. The one I had before was a full cheek but again not sure what type, but its not harsh at all, that why I changed it to the harsher one I have now. It could have been the bit but when I first got him I used that bit and it was fine so idk. I have noticed small cracks at one corner of his mouth so perhaps it's the bit, but it may be resolved now that I have changed it, we will have to see speaking that I don't return home from ny until Friday night. He has a sensitive back but I know for a fact that its not the saddle cuz that was his previous one prior from when I first got him, it was specially made to fit his back, so it's not that. And yes I agree it was stupid to gallop him around like that but when your POed u do stupid things lol. When I was bringing him down from the gallop he wouldnt listen so yes, I did do a one rein stop. And yes, he is very well trained in circles but his previous owner only did circles with him so I'm trying to expose his brain to other thing besides circles.
Sounds like you need an instructor who can actually help you - one who just backs off because your angry isn't helping anything. It also sounds like you know exactly what you should do to help him calm down but chose something else? When exposing a horse who's only ever done small figures- to big figures, he'll need time to realize he doesn't need to race through it.
As for the bit! YES if there are cracks on his mouth his bit is seriously not right for him! What mouth piece is in his mouth? Full cheek and D ring are only slightly different, but the part that's in his mouth is what really effects him. Does it have a single joint? The single joint could be hitting his pallet if he has a low pallet. Was the previous one double jointed?
Honestly, if a horse is acting up- using a harsher bit is the worst option IMO. It just hurts them more.
If a horse won't respond to the bit your using he needs to be better trained, the only time to change bits is if they're not comfortable in a bit or if they're learning a new skill that would benefit from a more clear bit - not because they stopped listening to the first.
Give him his comfortable bit back -Go back to the basics, walk trot, don't even canter, work on small relaxed figures, gradually, slowly making them larger, adding short straight lines. Whenever he starts to get worked up go a little smaller on your figures.
The next crucial thing for you to remember - the more worked up you are the more worked up your horse is. The angrier you are the angrier he's getting. He's saying "dammit MOM Can't you see ____ is wrong?!" and you're saying "dammit horse can't you see you need to do ____?!" But neither of you are listening. So take a deep breath, relax - do it for your horses sake. Soften your body - focus on happy thoughts, remember you're riding your horse and this is awesome! Not many people get to have a horse of their own they can ride all the time, you are lucky and this is fantastic and fun! Enjoy it! Horses are supposed to be enjoyable. Everytime you think of something negative fight it.
"I'm so happy I can ride my pony, he's doing a good relaxed walk" if your thought turns to "but he wont___" Quickly change that though to "but he is ____ ___ and ____"
So fix your bit, relax the horse, relax yourself and take time to enjoy your horse