Hi, I just wanted to give some support if not so much advice. I have a very similar story in that I had never competed or even danced much ballroom before I started my teaching training. I was teaching ballet and modern (contemporary) and pilates and went to a Fred Astaire that was advertising for a new ballet teacher.
It was a very small Fred Astaire in a small community in Ohio and they really helped me a lot to get my teaching qualification quickly (but I had to work hard for it). I taught at Fred Astaire for two years before moving to the UK. I've recently started working at a studio in London who were more impressed with my drive and teaching ability than my technique and are now apprenticing me to get my ISTD exams.
I have done a few competitions now and am hoping to do more- starting to train with a guy at my studio. I always feel like I don't have enough qualifications or an impressive resume but if you have the passion, you can do it. You just have to prove to people that you want it and you have to work hard.
Now, I am in the studio everyday practicing so I can take my exams as soon as possible and the owners know that even though I can't teach many lessons now, I will make a good teacher because I am dedicated.
So, hang in there, you just need to find the right people to help you out. And don't write off Fred Astaires or Arthur Murrays- there are some good ones out there and they can be a good springboard to something else.
Good Luck!