I go thru this a lot also. I'm afraid of being wrong, or offending someone. When I do talk I feel inferior, or fear that I said something that upset someone.
The other day I was in a store and a friend came up to me. She started talking to me, and I said something I afterwards feared I had offended her, or maybe just sounded stupid.
I feal guilty because I know what I said was said wrong in some way.
I do this in chat too. I sit back and watch the conversation go by, and say I'm ok when asked. Its never been ok to be anything but fine. I'm not used to letting anyone know me.