Keep rewriting until you're positive you've made it as scary as you possibly can. The personal fantasies of that writer. This can include various genres, but they all share certain common elements. They're of interest only to the person who wrote them. They're laughably trite.
All realism is sacrificed for the gratification of the writer's thinly disguised main character.
They tend to involve people, situations, and acts that should never be allowed out in public. Some writers start out writing such things, just because they need to write. The ones who become successful learn how to write quality fiction, using the early stuff to line birdcages or fuel their fireplaces. Here's an idea. This encompasses all of the above and then some.