I have done this block many times, sometimes using scraps and sometimes using jelly rolls. I am pretty sure of my ability to do an accurate 1/4" seam, but often my blocks don't match up like I want them to. I have found that the little culprit is my pressing: I have a bad habit of not working carefully and slowly to make sure the seams are truly flat. I get in too much of a hurry, I guess.
Please don't be too hard on yourself. Take it slow. Sew steadily. Press well. Cut accurately. You'll get through all of this and create a colorful masterpiece at the same time.