What do you think of my scary short story idea?

It sounds good. I'd say go for it. :) It's hard to pull off horror stories, so make sure you focus a lot on emotion to try to get the reader really involved. Would I read it? No, but that's only because I'm not a big fan of short stories. But... the only thing I wouldn't particularly like about it is the fact that you use a girl as the hostage. Girls always seem to be taken hostage, why can't a boy ever be taken? It's the "Damsel in Distress" thing going on that I absolutely personally despise. But, it's still a fine idea.