Lines 11-15 Summary

Get out the microscope, because we’re going through this poem line-by-line.

There are no curses, only mirrors
held up to the souls of gods and mortals.

This is the first time the poem has played around with form; line 11 is indented a little. Notice how it begins in the space where line 10 ends? This is a clever way to use enjambment to encourage the reader to keep reading without pause.
Dove also uses alliteration here ("mirrors" and "mortals") to give the poem a little music. Check out "Sound Check" for more on this poem's sound.
Now back to the drama: instead of cursing Hades for stealing her daughter, Demeter says he'll just have to look in the mirror. Say what?
Perhaps that's punishment enough for him to have to face himself every day, knowing how he hurt the world.
She says that there aren't any curses at all; that people (and gods) just have to deal with the repercussions of their actions (oo, cold burn Hades).

And so I give up this fate, too.

We admit, "give up this fate," is a bit of an ambiguous phrase. We mean, how can you "give up" your fate. After all, it's fate, right? By definition, fate's one of those things that you just can't give up.
One way of looking at this line, though, is that Demeter is surrendering (giving up) to this same fate that our man Hades is subject to. In other words, she, too, will be faced with this symbolic mirror.
After all, she's the one who decided to refuse to let anything grow during the times that Persephone is in Hades. She's the one who took revenge on the earth, even if it was because Hades wronged her. Just like us, Demeter isn't exempt from the repercussions of her actions.
She's saying that it's just the way the world works, whether you are god or mortal. (In the meantime, though… couldn't she maybe let a few things grow again?)

Believe in yourself,
go ahead—see where it gets you.

So, is Demeter asking Hades to continue to believe that he is doing the right thing, or just asking him to continue believing in his own powers? Either way, these lines read like a threat— especially with that long pause after "go ahead."
We bet, when you read it aloud, you naturally complete the phrase with an "I dare ya. And essentially, Demeter is daring Hades here.
Keep on acting selfishly, she says, and you'll be faced with even worse in retaliation. Remember that, back in line 1, Demeter is wishing knowledge for Hades. It's not that she wants him to stop acting like a god, or believing in his own power (after all, it's hard to get a god to do either of those things). Instead, she's wishing for him to realize just how awful his actions can be for those around him. So, believing in himself and wielding more of his power can actually lead him to a more intense realization of just how destructive he can be. (And remember, too, that Dove is not just having Demeter talk to Hades, she's talking to us readers, too. We all need to face the mirror to examine the impact our behavior might have on others.)
And that's it. There's no "amen" at the end of this prayer. Demeter's said all she needs to say.