try… entering the poem in the CODE tab

line breaks should be recognised, and you can use minimal HTML (like line break tags) and non-breakable-space sequences (to indent)

Line break char:
<br>

NonBreak space char:
&nbsp;

Centering can be easily achieved by using center tags around the text:
<center>
text to be centered
</center>

<hr> - produces a horizontal rule

Remember - MUST BE in the CODE tab.