You've abused the word "Suddenly". This is lazy and should have been beaten out of you by your fifth-grade english teacher. Avoid trite words and phrases and your writing will be much better.
Other than that, and one or two typos, the grammar is good.
The story has nothing new, so far, but is a good enough example of its genre.
That is, until the very last paragraph. The last paragraph makes Harry out to be brainless and even less mature than he was as an eleven year old!
This story is not bad but has room for improvement.