I have trouble making my seams line up too. When they are off some, one has to resew ( another cuss word) the block, or ease the larger block into the other, matching the seams inside the block. It really helps to make sure your seams are consistent, mark the points where anything is supposed to meet before you sew it together, and make sure they match when you get through. Also measure your finished blocks before joining.
I am going to try both of the methods mentioned above and I am looking for those pins next trip to town.