Your story is quite original and an interesting read. But there are two things I noticed that you have problems with: proper transitions (one moment Harry is in one place, the next we are in a totally different place). And a proper explanation of backgrounds (It still isn't completely clear to me how Harry finally managed to escape, where he suddenly got his metamorph-skills from, what other items he suddenly has and where from, etc.) A lot of time you describe something as "Harry has this or that." - but not much explanation as to where he got it from.
That detracts from your story a lot more than the minor grammar or spelling errors you have.