I wanted control over the INNER edges of at least two of the inner 'edges'. I created two horizontal lines on the squedge with tape where the edges of a couple of the strips are sewn. That way each time I line up the squedge I can check the angles between the upper and lower edges.
I found that with my horizontal lines I can check how well I pressed my strips and get better angles.
See the photo below. (Pardon the ugly spots leftover from using duct tape on the back in the past!)