My concept was changing rapidly too, right up until Term 1 Week 3. So I frowned, crossed out the word 'change' and put 'evolve'. That way, you can say how it progressed in your Journal and how you built upon it.
Now, when I felt the concept was clutching at straws I evolved it until I had written enough to set it in concrete.
Mind you, all you story-writers, there is no word count for websites or Multimedia. You could just put your story on a screen, add images and music, and have a word limit not constrained to 8000. Its brilliant! Not that I'm doing that though.
Of course, you have to maintain quality, but I've seen a really good website with over 20,000 words get 49. You just have to have 15-40 screens of 'substantial text.' I would still like to stick to under 10,000 though. It's analytical-imaginative writing.