My most unforgettable experience in China was a sleepover in my friends house. We played watergun fight and play other fun games. It was my first sleepover and the last sleepover there. This is my most unforgettable experience in China.

Corrections:
1. Proper tense of the verb (is = was)
2. Repetition of the same word in a sentence or paragraph (If the subject was mentioned already we could omit them in a sentence or use proper pronouns for the next sentence.

Thank you for doing your homework, Daniel