You started of great, very face-pased very intriguing.... in my opinion, there is no reason to devote chapters to how he got there, you can stick that bit in the conversations betweeen him and say... Remus or Hermioen/Ron when he gets back. In other words, i'd suggest you
1) begin from where you left off at chapter one
2) begin from september first.
i really think we've all read enough summertime growing stories to know the gist of what could have happened, and naturally, you can preodically furnish us with details.