I am going to presume those doing this Quilt-a-Long with me found Block 1 and 2 as easy as I promised. Hope the scant 1/4″ was easy for you to determine. The 3 fabric strip test is the best evidence if your seam width is right on for your blocks to turn out the size planned. For instance, the blocks you just made should be 8 1/2″ and will be an 8″ square finished (in the quilt top).
Now for Block 3, you will need your bag of 2 1/2″ x 4 1/2″ rectangles. 2 light, 2 med light, and 4 dark is what makes up this block. Each light and med light will be paired with a dark. Stitch a scant 1/4″ on the long side, press open with the seam going to the dark. Follow the photo below for how the 4 units will be put together to make this block. Work in rows, stitching the top 2 units, then the bottom two, one right after the other. Cut the thread at the machine, but not between. Open the rows, press the top row seam to the right; press the bottom row seam to the left and they will nest nicely when you sew the rows to each other.
I know, another easy block. Wait until you 
see Block 4 – Jewel Box!