Welcome Stevie! I love your outlook :-) There are many things much worse than MC.
I started having symptoms when I was about your age. We didn't know what was wrong until I was in my 20s. I just compensated and did most of the things I wanted to anyway. I loved roller skating, horseback riding, swimming (lifeguard), bike riding and music (band and choir).
You might want to reply to Violet's message from a few days ago (Titled "Heyy"). She's 12 and looking for someone to talk to with MC.
Unfortunately, I'm not not 9 anymore...I'm an adult now, but when I was 9 or 10 I started to have really bad myotonia. I see you have Thomsen Myotonia Congenita, the dominant form of the disorder. Does anyone else in your family have it? I have Becker myotonia congenita, the recessive form, so I'm pretty much the only one in my family with it and I've never met another person with any kind of myotonia in real life.
I can't think of anyone off hand, but I'm sure some of the members here with Thomsen MC probably have a kid about your age who also has Thomsen MC.
Do you play any sports?
When I was your age I used to be interested in playing a lot of different sports but I couldn't move well enough to participate in most of them. I did karate for a while though believe it or not.