I'm surprised the poly package says to quilt that close. Poly battings I have used have been more than that.
Did you mean tying each corner of each strip or each corner of the 12 blocks? I usually tie a quilt with poly batting about every 6 inches depending on the pattern and where I want the ties.
You could machine quilt stitch in the ditch too. It would depend on the size of the quilt and the throat space of your sewing machine.