What does Gorman mean in this stanza? What is she saying?

While I agree with the general meaning of this poem- that we as a country still have a long way to go, I find the last line a little odd. It suggests that she is limited to writing and reciting poetry. But in fact, she's very young, and actually ineligible to run for president, and there's a partly Black woman in line to be the next President, so the negativeness about her own situation is unwarranted. She's right in general, though. 

The closing lines are a not-so-subtle reference back to the "unfinished" nature of the country observed in the third line.  It's great that a young black girl can dream of being President, but she makes it clear that the dream is as of yet unattained in reality.

In short, she is saying "we've come a long way, but still not far enough."

She is saying that we as a nation are a work in progress.  There is work to be done to achieve our ideals.  We have inherited a country at this time, where a young black girl can dream of being president, but is unable to realize that dream.  We have not progressed beyond that point at this juncture.  It is not that we are broken, we are still evolving.