It’s actually NORMAL to make mistakes when you’re learning a language.
Even your FIRST language! For example, when children are learning the past tense in English, they make mistakes like “I falled down,” because that’s how the general rule works, and later they acquire the irregular form, “fell.” Don’t believe me? Try listening to kids for a while. Then try listening to adults!
How can you be expected to speak perfectly all the time, especially when you’re learning, and don’t know a lot of stuff yet? This can scare people into not talking. Let’s not blame your teacher; in my opinion, requirements from schools and states often create unnecessarily stressful environments.
If the editor in your head is on all the time, and you’re spending all your time trying to fix your sentence in your brain before speaking, the other person will move on and talk about something else, and you’ll have lost your opportunity to get a word in. It also makes it harder for you to listen to the other person.
It’s much better to focus on the conversation—what you and the other person want to communicate to each other. Now, I’m not saying you should completely turn off the editor in your head: express yourself as correctly you can. Just don’t let it get in the way too much. Have fun!
[In case you feel like reading scholarly papers, these ideas are based on linguistic research on error analysis (linguistics) by Noam Chomsky and others, and Stephen Krashen’s theories including The Monitor Hypothesis and The Affective Filter Hypothesis.]