Creating Child Theme from customized original.

I am trying to make a couple of changes to the Twenty Eleven theme that I cannot change using Appearance (like font sizes, spacing, favicon location Etc.) and when I follow the instructions to create a Child Theme here I see the original version of the Twenty Eleven theme and not the customized version I created by changing settings in Appearance and uploading new backgrounds, header images Etc..

Is there a way to make a Child Theme from my customized version of Twenty Eleven or do I need to make a Child Theme that points to it, redo the changes I made in Appearance and then add changes to the Twenty Eleven code in the new Child Theme style.css file.