You can use the "poor man's copyright" to protect yourself. When you finish writing, don't publish right away, but make a printed copy of your story. Put it in an envelope and mail it to yourself. When it arrives in your mailbox, DO NOT OPEN IT, but place it in a safe place. THEN publish your original work.
Should you ever experience copyright infringement, the sealed envelope and postmark from the post office is sufficient evidence that the material in the envelope predates first electronic publication, which should be yours, since you sensibly waited to publish until you had proof of copyright.
This method has been used to successfully demonstrate copyright in a court of law.