OK, go through the work and see if there are places which feel thin because you have told the reader how a person is feeling eg he was feeling nervous.
Now you can do two things that will strengthen your work -
1. add more words
2. show the reader how they are feeling by describing what the person is doing and what they are saying and leave out any reference to telling how they are feeling.
So you can say:
His fingers seemed anchored between his lips. The rhythmic crunch of breaking nails accented the dance from left foot to right and back again.
Four words just became lots and you get a stronger picture in your head. And not once did I say he was feeling nervous, but you can see it (I hope).
Also, read it through and see if you can see the movie in your head. If not, what's missing? Description? Dialogue? Dialogue can add words and also strengthen a story. But, don't just add words for the sake of adding words.
Also, adding a new character can increase the word count because you have to:
1. Introduce them
2. describe them
3. include them in the action
and so on.
Hope that helps in the time you have available.