What was I working on last week?

OMG, as I mentioned last week, I’m writing book two for NaNo. I’m seven chapters in, and I think I started telling the story I’m meant to tell about 1 1/2 chapters ago.
There are bits and pieces before then that belong, like Kiara and Dakota having a fight and breaking up, but why did I feel the need to go on for three chapters about the twins starting a new school?
I was talking to a Ninja staff member yesterday, who asked me a very important question: How can you know where to start book two when you don’t know where book one ends?
Crap. I know where book one ends right now. That doesn’t mean that’s where it’s going to end when I get the edits back from my editor tomorrow.
And around in circles we go again.