May I ask why you feel all your chapters need to be ~2500 words? My friend was saying how he tries to make his chapters around 2000 words each, and I explained to him that chapters don't need to be a specific length. I linked him to this article I had found and I think it might be worth linking it here just in case anyone has strict ideas about how long a chapter should be:
http://allwritefictionadvice.blogspot.ca/2012/05/chapter-novel-lengths.html
So if your current chapter is 1.2k words because that's how many words it took you to write that scene, then I'd say, don't feel like you need to "stretch" it to 2.5k. Let the chapter end where it feels right, and then move on to the next chapter. Maybe in the revision process, you'll find a way to extend it another 400 words or whatever, but part of the challenge of NaNoWriMo is putting you under enough pressure that you can't afford to spend extra time over stuff like that. Deadlines! Rawr!
I read the article, and I'd have to say I agree with it. The only problem is, I've decided my chapter is going to be 2500 words because that's what it needs to be.
I've got a short summary for all 20 chapters in the story I have planned. And because maths, 50,000/20 = 2500. So,
on average, each chapter should be around 2500 words. This makes it easy to set a daily (or in this chapter's case, bi-daily) goal: 2500 words. That way, I have a little breathing room.
Now, I understand that each chapter won't be
exactly 2500 words. My first chapter was closer to 2700 or 2800, and my second was closer to 2600. While I could count that as 300-400 words that I can have "in reserve" as a buffer if a chapter isn't 2500 words, I'd rather have it the other way. That way, even if I don't finish the story by the end of November, I've reached my 50,000 word count.
I'm working around it, though. The bulk of the chapter was in the first 1,000 words, so I'm devoting the other 1,500 to character development. I definitely need some, I can fit it into the chapter I'm working on right now without too much trouble, and I'll reach my chapter quota. Everyone wins!
I know, I know, I shouldn't "bulk up" the story with needless information. But, I've come to the conclusion that I need to develop the main character here, so I will. No hard feelings; in any other situation I probably wouldn't have this problem in the first place. I'm not trying to disagree with you; I just have a schedule that I've made, and I plan on following it.
-Wallace
(I spent too much time replying to this, I've gotta go write stuff now.

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(Oh, and if you want, I can PM you my chapter summaries. Because it's more of a guide for me than anyone else, some stuff in it might not make sense, but you can still read it if you want.)