Hey Nemo. I used to be almost exactly like you in terms of wanting to communicate perfectly. It's amazing how much you said in your post that I can directly relate to. I feel like I was left out big time in terms of socialism. And whenever I made a mistake like talking too quietly, I would feel like I lost all respect from the person I was trying to socialize with. One of my biggest problems was starting a conversation though. Because I have overcome many (not all...) of these crippling social problems, so I thought maybe I could help you too. Here are some things you could try around a new group of people you have never been around before:

1 Remember you do not have to talk to everyone, at every time of the day.
2 Always try to make an excuse to start a conversation, as soon as you come into contact with a new person as possible. Even if it is a dumb reason. This will make people overlook your conversation "mistakes", because their first impression of you will be that you are open enough to begin talking.
3 Pretend like nothing offends you, and that you do not take anything seriously. I often smile when someone insults me and be like "Huuh?? " even though I am secretly thinking something maniacal such as "I would be fond of popping your sweet eyes out right now". It usually turns out the other person was only joking and often jokes the same way with other people too.
4 When you know someone does not like you, or when you suspect it, do not let on. Interact with that person the same way you always do. Eventually they may even forget why they dislike you. People are pretty shallow when it comes to this stuff if you ask me. It's all about how they feel.
5 Remember that you will often encounter rude people. The best way to deal with them is ignore them and pretend like they do not phase you. Do not allow yourself to contemplate the stupidity of others, especially if you do not have to interact with them again.
6 Do not give up on conversing with a person because of your mistakes. If you do not ignore your mistakes, people will think that you have stopped talking to them because you do not like them. Remember, if you are frowning, extroverts are likely to think it is because you do not like them rather than you are tired or upset about something that does not involve them.
These are things I have learned from experience. You can tell I have a rather low opinion of humanity.. Anyway, I hope something I said can be of assistance. Good luck to you.