Carefully press your blocks using a bit of starch or best press, gently pulling them into square. Next, measure and find the smallest block, then cut them all down to the same size. If one or two blocks are way way smaller than the rest, your seam allowance is probably off and you should take those blocks apart, press the pieces & re sew. The pattern is very linear so making the blocks as square as possible and all the same size will give you the best result.