At those kinds of intersections, I don't just backstitch through the two strips I am joining; I also backstitch through the third seam allowance. Not sure I can describe what I mean very well.
The construction method you described is typical for machine piecing, but is not the method I would use for hand piecing this block. For hand piecing I start with one piece and add on one piece at a time. Where there is joining of three pieces, I secure all three pieces at that join.
Clear as mud???