We don't write letters for people, monchele. I suspect that even if we did, your teacher would soon realise that you hadn't written it yourself and would wonder about your sincerity.
Your grammar is not bad at all. Write from the heart and keep it short. As she's your English teacher, you can make her feel good by spelling 'truly' right, not using 'kinda' and avoiding writing three exclamation marks together.
Student or Learner