That is what NaNo is all about. We all say we don't have time. I thought so too last year, but if you don't try and just do it, you will never know.
The story doesn't have to be great or perfect or anything. Nobody has to read it, not even you if you don't want to. After November you can throw it away, but if you reached the 50000 you will be really, really proud of yourself!