Lots of good ideas! I try to put the right side piece over the left and put a pin (or a clip) on that seam at the top edge. Then go and sew it. You could do a whole row like that to the machine and sew them all at once. Then take them back to the design wall and see if they are correct. Every once in a while, stand back and admire your work. Did you do it right.
I have had a quilt on my design wall almost finished and had it hanging there for a few days while other things were going on. Then I saw that something was wrong. It takes a while sometimes for thing to pop out at you. Better to correct it while it's still a flimsy.