Hi thank you, I do have a child theme.
Off topic a little bit: you really don't. Which is completely fine BTW. :)
What you have is a copy of the Twenty Eleven v1.3 theme.
That will prevent Twenty Eleven updates from wiping out your work (different name and different directory) but it will also prevent you from getting bug fixes as well as any security updates for that theme (if any pop up).
If you can identify the CSS you've changed then you can create a child theme and just put those changes after the
From taking a quick look at your CSS it looks like you're changes can go into a child theme
style.css file like this one.
But I wasn't able to incorporate your changes exactly. The font color is off but doing a diff between your
style.css file and the Twenty Eleven v1.3 file that's what I came up with.