Well, to a certain point, copyright is yours since you create it. But if it is not registered, it's difficult when a claim arises.

But, yeah, a good thing to do is organize your writing and send it to the copyright office, even if it's not meant to become a book.

You can name it just for the sake of records, and send it with the $30.00 fee. That ensures you have your material registered, and should any claim arise, you have proof it is yours.

It takes a few months to get back the certificate, but it's effective on the postmarked date-when you send it in.
It is definitely worth it!!! And it gives you peace of mind.

Registered with the copyright office or not, you still need to be careful where you post your writing!

But we learn as we go, so you're not alone, as frustratring as your experience is.

Hope this helps!