I don't know how many have this book but lots make granny squares so here is my answer....
First, if you are not the person in question, I will not post the entire pattern as that would be infringing on the owners copyright. But for explanatory purposes of the question, I left what she had written about round 8 so we would all be on the same page which, in the book, happens to be pages 138-139, and 162-163. The book is from "American school of Needlework" Volume 2 book 1336.
Please excuse the dots of blue paint on my nails and under them; it is from making a floral arrangement yesterday and I have to wait till it wears off. See previous post about work fun.
Ok, on to the question...
First off, on the previous round you only have chains in the corners on the sides of the granny; there are no chains, just sets of 3 dc.
This is different from the previous rounds. Just making sure you have the previous row correct. For some reason for the set up of the edge the author has you sort of decreasing by removing the chains in the previous round. That is a side note back to question.
You slip stitch into the space that the two chains made on the corner; do not slip stitch into any of the chains.