Uh oh! Before you freak out, see if any of these things might be happening:
Be sure you’re writing a chapter, not a note. Notes have striped lines through their titles and don’t count towards your word-count. Open up the note settings by clicking the wrench next to the note title, then change that note to a chapter.
Be sure you selected the option that said you were going to write on the YWP, not the option that said you would type somewhere else and update your word count manually. To check or change your setting, click the wrench at the top of the novel box to open up the novel settings.