I feel nervous when I speak English with my teacher because I concentrate too heavily on grammar. What should I do?
Forget about the grammar, concentrate on being understood. The grammar can come later.
Think of this example: A tourist approaches and says in perfect, fluent, and unaccented English: “Why, how do you do my good sir, I would awfully appreciate it if you could kindly refer me to....” but cannot remember the word for “railway station.” Then consider this example: A tourist approaches and says with a heavy accent, “Excuse... Where.... Train”.
You would be able to help the second tourist, and guide him to the train station. You can’t help the first tourist, as you have no idea where he wants to go.
There is no use having good grammar if you can’t communicate.
Darren McSweeney, amateur speaker