Maybe it didn't have a fulfilling ending or the story lacked depth. Sometimes, if the characters' development isn't satisfying, it can leave you with that empty feeling.
Scary stories can make you paranoid because they often play on your deepest fears and imaginations. They trigger your brain to envision threatening scenarios that might not exist in reality.
In the modern romance novel,"The Exclusive Bride of the Overbearing CEO," the relationship between the female and male lead was like,"I don't care if it's hell or heaven. As long as it's a place with you, I'm willing to stay by your side and accompany you forever." The feeling. I hope you like my recommendation. Muah ~
To make your story longer, you could incorporate additional conflicts or challenges for the characters to overcome. Also, spend more time on the settings and world-building to make it more immersive.