Sure, here is an 8-sentence self-introduction in English for a middle school student:

Hello, everyone. I'm glad to meet you all.

I love to read books, especially science fiction and fantasy novels.

I'm also interested in music, and I play the guitar as a hobby.

My favorite subject is math, and I hope to pursue a career in engineering or science.

I'm passionate about learning, and I enjoy challenging myself to improve.

Thank you for listening to me, and I look forward to making new friends and learning together with you all.