Dear...,
I'm sorry that you failed your exam and your teacher warned you about that. I'm worried about it and I hope I can give you some help. As a university student, you should spend more time on you study instead of dreaming all day. An old saying says, "No gains, without pains." Nobody can succeed without hard working. So I think you should listen to your teachers in class carefully and read more books in the school library in your spare time. So long as you work hard, you will be successful soon.
I hope you will make progress in a short time.
Yours sincerely,
...
relieved as she jumped behind