Protect your work through the Library of Congress. Just go to their website. You'll find links there that will get you in the right direction. It's not a difficult process. There is a charge, but if you are that worried about someone stealing your work, then it should be well worth it your piece of mind.

You may also simply Google "copyright form" and the first line will guide you to a download form. You will first need the latests Adobe Reader download ("Adobe Reader 8.1.1" at the time of this writing.

If you have difficulty downloading or printing forms, you may also request Forms by Mail or by phone (202) 707-9100 (not toll-free).

As to writing "copyright" on your copy, a better way to do this is "Protected by U.S. Copyright Law." as exemplified at a website, www.onealclan.com/inherited_trait.htm" or "www.onealclan.com/day_dinosaurs_died.htm". The concept used therein is that your work is protected, whether copyrighted or not. However, the concept of public domain may be arguable in a court of law.

Obtaining a copyright is inexpensive and easy. Good luck with your literary work.