Next, cut a 4in. by 4in. square out of each corner
We then laid a piece of scrap selvage edge along the length of the blanket edge. Then we cut 4 in cuts into the blanket along all four sides- moving the scrap as we moved around the blanket--this keeps the cuts even. I have heard that some people use masking tape to mark this cutting line, but it didn't seem needed, and my 12 year old did just fine with the scrap of material.
At any time you could pin the front and back together to prevent the material from slipping. I added a few pins just to make sure it didn't move while we were tying the blanket together. I probably won't do this again because it didn't seem to want to "move" at all.