Are you nesting your seams when you sew them together? If you iron your row seams in opposite directions and then sew them together with the top seam facing away from you they will "nest" together quite easily and your seams will look nice on the top.

Here is a little tutorial on how to nest your seams and how perfect they turn out when you do!
http://quiltcetera.wordpress.com/201...-a-four-patch/