You mentioned that you pressed to set the seam then pressed seam to one side. Do you use steam when you press? My fabrics look much better if I do not use steam when pressing the seams and blocks.

Are one of the pieces cut on the bias? If so, you might be inadvertently stretching or pushing the fabric so they match up. I would look at all of these tips, as well as the pressure of your foot, it might be pushing down too much on the fabrics.