I wouldn't go back and insert the additional content there. That would lead to too much temptation to start editing, and the next thing you'll know, you're stalled at 30,000 words on November 29.
If you want to, make a note for yourself in the text. Such as, in big bold letters,
GO BACK AND FIGURE OUT HOW TO SQUEEZE THIS INTO CHAPTER TWO. Then write your scene from there. I know that there are some who like to take the linear approach (like me) and write a story from beginning to end. But there are a lot of other writers who take more of a scene-based approach. They write the major scenes they want to appear in the novel, then they rearrange them into whatever fashion they want. Once they have their scenes laid out in the chronology they think would work best, they go back and add in the filler details to actually connect the scenes. Occasionally, they may rearrange the scenes during this process so it seems more orderly to them. This approach is actually analogous to the idea of the movie producer or director that we discussed earlier, since it's similar to the way they work.
Here's one example that I just completely made up. Let's say you're writing a mystery novel, where your main character is a detective, but she's a bit of a slob. You write a detailed explanation of her messy apartment, and have her sitting on her loveseat watching a movie, by herself. She accidentally drops her steak knife, and as she bends down to pick it up, she kicks it under the loveseat. "Meh, I'll pick it up later," she thinks, and goes back to her dinner and movie. In the climactic chapter, the serial killer is in her apartment and punches her in the face. She collapses on the ground... right in front of the loveseat. She remembers the knife that she had kicked under there, manages to grab it, and uses it to subdue the serial killer.
These two chapters could be several hundred pages away from each other. But you could write them back-to-back so all the details are fresh in your mind... and so you don't forget that important plot point of the lost knife. What started out as a minor depiction of how much of a slob Miss Detective is becomes critical later, but it's something that you don't want to overlook - especially since
you might forget about that knife after several hundred pages yourself!
Don't get into the mindset that there is only one way to write a novel. After all, there's not just one way to paint, or sculpt, or film movies. Don't be afraid to experiment a bit and see what feels best for you.
Addition: You're well ahead of me in the word count department! I need to try to catch up to you. Don't slump now and let me pass you in the race!
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