Nothing wrong with your English here, so it seems more related to your issue with public speaking.

If you have noone to speak English to, try "narrating" yourself in English when you are at home by yourself. Just voice everything you are doing and/or thinking in English. This will help you get more comfortable speaking it.

Also, try talking to your teacher about your issue with introversy / public speaking if they are in any way approachable for these things, and ask them for other tips in trying to get used to speaking English (your writing seems more than fine) - tips other than "you just have to get over it", ofcourse. They night have some good resources for you to use.

Related, but irrelevant. This is why once I started gaming online, I always looked for international groups / communities. It got me used to speaking English all the time.