You should have a 'half fat quarter' left of both your fabrics from making your checkerboard top. You will need both of these for this part. Cut each of these 'half fat quarters' into 8 squares that measure 5" by 5". You can make yourself a paper template again if you like and draw around it onto the fabric, or you can just draw your line straight onto the fabric and then cut them out.
Do this with all 8 pairs of squares. Then cut along the drawn line:
But when you are happy with your arrangement, sew one row at a time together, with right sides together. Then press all these seams. Try and alternate the seam pressing and if you can also press towards the dark side. Then sew all your rows together to make your finished cushion top.