Great chapter, are you going to go though the fouth year or do highlights of it?? But if you going for his forth year, then Harry meant to be 13 going on 14 not 12 going on 13 Befread. If you want info about dates and all that go here http://www.hp-lexicon.org/index-2.html it'll help you a lot.
And Befread Harry didn't blow up Marge in the beginning of his second year, it was his third.
And as for this part 'Harry, you’re only done second year,' I think it should be third year if you are going to do the fouth year. This is unless you're doing his third year first.
Author's response
Thanks man. I'm pretty new with HP fanfiction writing so all the information helps.
I'm only going to highlight his 3rd year, the actual story begins after the summer before his 4th year.