in piecing a block with so many seams, it is important to test to make sure each part is finishing up the size it should be. At this point, I suggest you measure the block and square them up and then measure to determine how long the sashing should be.
For instance, if they should have finished at 10.5" but didn't, then work with the new size. If they finished at 10" then the sashing should be 10" etc. I hope this is clear.
The posts have indicated what the problem might be - seams not consistent, cutting not consistent etc.
sewing patchwork is only as good as the last seam.
And....don't assume the 1/4" foot is accurate but mark where the seam allowance should be not where the foot says it is.