Did you wash/dry your fabric, before cutting and sewing? Sometimes fabric is stretched a bit out of shape, when it's put onto the bolt. Washing returns it to it's 'natural' state, which can often cause distortion if it's already sewn into place.
Other than that, I almost always use W & N and usually quilt at about 5" - 7" apart (straight stitching). It always puckers a bit when washed, but the puckering is always uniform, across the entire quilt.