I posted the first chapter of another book I'm writing called Fire Phoenix, I know you will like it. The picture has a girl that's made of fire. Hope you love it! :)
Go to 'My Works', click to edit the story you want copyrighted (or, in your case, poem), and then choose the 'Advanced' option. You should then see the copyright option.
OMG thanks so much for the amazing comments on my book! I really really appreciate it! You have no idea how much that made my day! Hopefully, I'll post Chapter 2 later tonight! <3