Hello,
can you please help me to complete our website, with the attached picture I would like to add 4 more content blocks,
but no matter how I try, I don’t get the desired result that only 4 blocks appear, a short feedback would be nice, thanks.
Hello and welcome to the Kirby forum. 
If you want to have a predefined layout with 4x3 blocks, complete your blueprint accordingly:
layouts:
- "1/4, 1/4, 1/4, 1/4, 1/4, 1/4, 1/4, 1/4, 1/4, 1/4, 1/4, 1/4"
The new layout is then displayed in the selection menu:
… and you have a new layout with 4x3 blocks:
You can find more information about the layout in the Kirby Reference: