How to make a story longer when you’ve already figured out the storyline and it’s too short?
It’s not easy but it can be done. I know because when I segued from short stories to novels I just about went crazy figuring out how to do exactly that.
The answer isn’t to pad your scenes. Readers will see through that right away. Nor should you add more scenes and/or chapters just to make the book longer. Again, readers will know what you’re doing and throw your book across the room without finishing it.
What you must do is figure out a longer storyline and make sure that that the added scenes become integral to the story instead of just being tacked on.
It’s hard but it can be done. Close your eyes and think what else could happen during the course of the story that will add to the story…