You are only 13, right? Correct me if not. Chinga was/is your first horse? And Pumpkin and Chinga are the only horses you have worked with?
Okay, sorry to be blunt here, but 1. You are too young for the majority of horse people to take you seriously as a trainer/rider, 2. You do not have enough experience for the majority of horse people to take you seriously as a trainer/rider.
One day I hope to be a trainer/breaker along with doing some horse dealing (buying, training and reselling). I have been riding since I was 5, and I am now 19. I have owned 6+ horses, and taken three of them from green broke to finished or almost there, as well as teaching those three to jump and event, taking one of them to A grade PC, when I passed him on as that was as far as my ability could take him. I instruct at Pony Club, have instructed at Zone 16 camp, and have been asked to travel to Pony Clubs outside my zone to teach Mounted Games, my specialty. I have represented Australia overseas.
Now i'm not trying to brag, what i'm saying is that even with the experience I have, I am nowhere near being confident to call myself a trainer or offer services to anyone without being asked.I still have a ton more to learn about my chosen disciplines, and am planning on taking a youngster from halter broke to finished successfully before I even consider offering my services to others.
Riding friends horses is a great wya to learn, and if you are helping, a great thing to do for your friends. But for other people, there are things to consider such as liability if you were to be injured, what would happen if the horse was injured while you were riding, etc.
If I were you, I would keep working with a trainer and Chinga; Riding other horses whenever the opportunity presents itself; talking to and learning from as many people as you possibly can; and be patient.
Personally I wouldn't want anyone even teaching manners to my horses unless they had either a record of success with other horses I know, or were successfully showing/campaigning/producing horses I like and like the behaviour of.
Do you have a consistent way of dealing with different issues? Can you adequately explain the process you will/would go through to an owner?
My best idea for you is not to offer 'training' to people, but offer to simply ride. The more horses you can ride, the better. Getting into Mounted Games enabled me to ride 100's of different horses throughout Australia and overseas and has taught me the majority of what I know about staying on and handling individual horses quirks, and training my own horses for many years has taught me what I know about gradual, stepped training. Now I just have to get out there and learn about 5x more!