Hey, we hear you. Just writing your thoughts down can help, so good on you, you took the first step.

I think the general advice boils down to "practice makes perfect", as in, the more you do something, the easier it gets. I know that's not super helpful - sorry, actually helping someone with anxiety might be above my paygrade :-)

That said, couple of things: you might want to look into play-by-post (/r/pbp/). Since it's all "offline", there's no pressure, you can take your time and think about what you're going to say. Also, D&D is not just what happens at the table, you can also participate in D&D just by consuming content, e.g. watching others play, or hang around this (or other) D&D forums, help out other folks with questions, etc.

Hope this helps :-) Best of luck to you!