My first questions would be - did you square each block up before you started? That can make an extreme difference. It appears that you are sewing all the way across or down your rows with a single piece of fabric. I have found that you will come up with different sizes and will be unhappy. If you measure your sashing to the exact size (i.e. 6" x 22" - if that's what the smallest block measures to) and sew on that on one both sides, then sew the 6X22 plus the block that should be 6x6 on the opposite side - you may have better results - anyway I find I have better results when I do it that way. I have a quilt top right now I have to take totally apart that I did in many years ago past and have kind of the same issues going on because I wasn't precise and when I look at it today I can't stand it (LOL).