I wouldn't worry too much about the direction of ironing the seams. When you put your groups of blocks together, you're going to be watching your pattern on the front (so you don't get 2 or 3 in a row the same) and you will probably move things around then anyway. I just completed a queen sized one with 4" squares, and as long as my seams aligned and I kept a reasonably random mixture, I didn't worry about the back. Yours looks great.