One possible version:

Hi! Mike,      

     Thanks for inviting me to your home. But I'm sorry I can't visit younext Satunlay. I'll be busy that day.

In the morning,  I have to doing my homework. I have too much homework. In the afternoon, I have

soccer training with the school team. In the evening, I am going to the movies with my friends. There is a

new movie. I think it's interesting and exciting. I can't miss it. Can you watch it with us next Saturday

evening?                

     Write soon.          

                                                                                                                                                Henry