Creating child theme for twenty eleven AFTER changing parent made

I used the twenty eleven theme, made some changes and then realized I needed to create a child theme. I created the child theme, but was unclear how to make more changes to the blank style sheet. So, I continued making changes to the parent theme. What would be the smartest next step for me to make?

How do I get the original parent theme back without losing the changes I made?

Would I create a child theme now and somehow revert the parent theme to its original state? if so, how do I go about that?

thanks!