Dear Mr Smith
  I am so sorry about that I didn't visit you yesterday. I am expectting you can forgive me . Yesterday, my fri LiHong got a bad cold , and nobody can take care of her .So I have to look after her and not have time to meet you .But i belive you can make sense of me . Because I am losed a important appointment ,I feel very sad. Can we have another meet ? I want to study  you very much.
  Looking forward to hearing  you.
  Yous,
  Li Hua