Penny got it right. Our first works often is something that comes directly from our psyche. But, just because it's dark, doesn't mean it's dangerous. Everyone has a little dark spot that we need to let go of.

For example, my first work published on Big Closet, the Half-Lilin series have all kinds of characters who are plain mean to the main character, but there are also characters who are helpful. I was able to write it because that was how I felt back then. But, that didn't mean that many people were mean to me in real life, it's just a story, based on what I felt back then. Unfortunately, my situation has changed and I no longer have that feeling, so I'm unable to write anymore Half-Lilin story. Don't read it though, I'm embarrassed at the lack of skill I had back then.

But as Penny said, just write what you want to write. If you yourself think it's too dark, label it something like 'Caution: Death' or 'Caution: Torture' so that people who can't stomach that can steer clear. It's your story. Unless you're planning on making it a commercial success, there's no need to think of what people want to read, merely what you want to write.

Some authors write to put their state of mind into form, so that they can better reflect on it. If this is you, there's nothing wrong with it. It can help clear your thoughts. I personally suffer from depression, split personality and sociopathic tendencies, causing me to having to rely on antipsychotic medications. Ever since I started writing though, I no longer have any need for the medications as I can create my own world in my stories, where I can act as any character I wish, from sweet little girls to evil demon kings. Nowadays, having vented most of my dark thoughts in Half-Lilin, most of my recent works are in the 'sweet and comedy' category.

If it's just your intention to write a scary and dark story and it has nothing to do with your state of mind, though, ignore most of the above lol

Still, it's your story. Do with it as you will. All the best.