"Khabazi: Generative Algorithms"- Clarification question

I've been working through the tutorials, but have hit a wall with the chapter on fabrication. 

I can't get the section components, to nest onto the sheet properly. (pg. 157, Figures 8.26-8,28).

I have the exact layout but have not  been able to get past this step. 

Could someone clarify a question:

Is the cutting surface introduced in Fig. 8.26 simply a surface?

One of the differences between what's on my screen and the book is the black box of "sheet_1" as opposed to the gray box. 

I'm wondering if this may be where i'm getting it wrong. 

Any help is appreciated. 

Thanks, 

Carlos