The teacher asked me to tell a story on stage, but I didn't write it, but what should I do if I am timid?

Exercise your courage. In fact, like you, I used to be very introverted, but later I found that I was no worse than others as long as I put my heart into it. With a successful experience, I have a sense of accomplishment, and then I can speak in public slowly.

I think you should make full preparations in advance and build up your confidence. If you memorize the manuscript and add some passion when you speak, it will be brilliant.