It looks to me like it's as much a stitching/seam allowance problem as a cutting problem. Starch, starch, starch. For some patterns, my fabrics are like little pieces of paper but it controls bias and helps with accurate seam allowances. Accurate stitching is hard for me so I use one of those barrier type seam guides. I mostly use my vintage machines for piecing so I use a magnetic guide.
I have also learned to square up as I go. Every block for sure and if it's a complex block with lots of units, I square up every unit. No one told me this and I struggled for a long time. Once I started squaring up as I go, my blocks got a lot easier and more accurate.
I would also suggest pressing your seams open. I've had pressing them to the side make my blocks off just a bit. Remember, if you have 4 seams and each is off 1/16" that means your finished block could be off a full quarter inch.