Well, as you’re saying: since you suddenly feel the need to change yourself and go a bit further to get his attention, he is probably a pretty great guy that means a lot to you. I get that it might seem completely terrifying to suddenly open up like that, but would’t how great he is at least make it worth a shot?
I’ve got admit that I have no real solution to your problem, but perhaps you could just attempt to decide that “I AM going to talk to him today. I’m going to be charming as hell and get his attention”. You’ve probably already been through such periods where you act really, really confident to get rid of the anxiety, and have probably also realised that even though you want to, that isn’t always as easy as it seems… But just make up your mind, know that you want to open up BECAUSE you know that in the long run it will most likely make you happier. As soon as those negative thoughts starts appearing, you could try to challenge them as much as you possibly can. “I might embarrass myself” Yes, but you MIGHT also make the greatest relationship ever. “He probably doesn’t even like me” Perhaps not, but what if he does? Being an organisation freak, myself, I always find it useful to write everything down (literally every single though that pops up. Literally.). List up the thoughts and how you would challenge them, and physically see that there might actually be a bright side to it all, as well.
Finally I think it is important to remember that very few of us are able to read minds or constantly know how to act in every single situation. Perhaps especially since I’m guessing you’re both sixteen? People can seem so confident and have these awesome comebacks when they're in their teens, but most of the time this is just words, isn’t it? I’m eighteen myself and I feel like this has been the case since we were around thirteen, maybe. Honestly it is probably going to continue to be this way until we get old enough to just stop caring so damn much how people view us.
I really do hope you manage to find a way to get to know him better. Worst case scenario: it turns out he doesn’t like you like that, but at least you did something incredible, considering your anxiety disorder; The outcome will be good no matter what, really. Best of luck!
(By the way, I don’t think sixteen isn’t too young in any way. Seriously: take it from a professional crusher: I’ve been crushing on boys since I was, like, four years old.)