No. Trademark laws don't have anything to do with that. It's copyright, but protection of plot lines and the like attaches to well-developed plot lines, characters, and the like. There's no way to protect story elements in the broad sense, just the specifics of how you're handling them, and only then to the extent of your development of them.
Registering does not prevent theft. It only supports legal action. I don't understand how registering the work has suddenly made it immune to theft, or how it will let you take legal action when you already suggest you can't afford it.
