First off, good job. Writing horror can be especially challenging, and you have really started this off well. (I also love the cover you made.)
Read the story now
When it comes to first person writing, make sure that Electra only thinks or states things that she would know or think, unlike writing with a narrator. People are usually not very self-aware, so including that in Electra's perspective will make her seem more relatable.
Feel free to let your readers connect the dots. It can often be tempting to overexplain or explicitly state things to ensure your readers understand. Though it is important for them to not be confused, if you let them make the conclusions themselves, it will give them a sense of accomplishment (and encourage them to keep reading.)
Don't be afraid to really mess with Electra's head. The more confused, disoriented, scared, and trapped she feels, the reader will feel as well. I'm not sure if you've heard of it, but check into Stephen King's three levels of horror. It's a great resource.
The scene with the bride was really well done. It was so detailed and descriptive and was very built up. Keep up the good work! (I can't wait to see what happens next)