It will be a good start, I would take the idea of 'not being good enough' out of your head though. start as now disabled said with no preconceptions or ideas, open yourself up to learning everything you can, you are a beginner no one expects you to do things perfectly or understand everything straight away so relax and enjoy yourself, while training is hard it can be enormous fun and you come away with a very legal 'high'. Like a lot of things there will be sessions you find frustrating but these get forgotten when you get it right. You aren't there to fight but to learn. See how you go, relax, work hard and enjoy, put competing to the back of your mind for a while until your coach says you're ready. Good luck.
Feel free to PM in a few months if you still want to compete and I'll see what I can do to help if you don't get it from your coach ( though you'll have to be honest lol and not say you are the greatest thing since sliced bread if you aren't!
) You can also Pm if you need to convince your parents that MMA isn't human cock fighting! ( such a rude expression if you think about it