Another possible 'problem' may be your fabrics. Are they all of the same thickness? Even the slightest weight difference can make a difference in how much space is taken, when pressing the seams. For heavier fabrics, you may need to press the seam flatter, or even press that seam to the opposite side. If the problem then shifts to the other side, try pressing the seam open.
If your blocks seem to line up before you start stitching, it may be your presser foot tension is off. It may also help to use your walking foot, when sewing your seams. Yes, I know that's a bit unorthodox but it often helps.
If all else fails, get yourself some Elmer's School Glue and put a tiny drop of that, at each intersecting seam. Set the glue with your iron, then put a pin through it, to hold it in place. When you stitch the area, ease in any slight fullness.
Last edited by Neesie; 11-12-2015 at 06:58 AM.