The third strip on the bottom row appears to be wider than the others, but it could be that your quarter inch seam is off. Once it's off, everything after it will be off and picking up more inaccuracy as you go along.
It just looks to me like you need to remove that bottom row and the third and sash and their two blocks.
Measure the sash strips and blocks and make sure they're the same size as the others and check your quarter inch seam and sew them back on the row and sew the bottom row on again.
Pins are our friends!
When I started, most of my problems were my seams. I couldn't sew straight and I couldn't sew accurate quarter inch seams -- even with the quarter inch foot.