When having problems lining up 1 1/2" squares, try using 1 1/2" strips instead. You have a little more control sewing strips together, and then can cross cut them into 1 1/2" units. Your seam allowance is critical. I use a magnetic seam gauge to line my fabric up against, like this one:
https://www.sewingpartsonline.com/ma...ide-gauge.aspx