Please, Please read my Harry Potter fanfiction! I think it's good!?

The plot is extremely cliche (especially in the Potter fandom) and it doesn't look like you've done much to improve on it. It's nice that you use understandable English and paragraphs (however short they may be) but by chapter three you toss it all out and just have dialog. NOTHING kills a story faster than the author trying to drive it through with pure dialog. Use descriptions, paragraphs, go off on a tangent! Anything as long as it creates substance.