its normal, the height and width of your knitted stitch is rarely equal, that is why they make 'special' knitters graph paper... i agree with artlady - your sample looks great! just take a step back from it for awhile so that you can see how pretty it is for all its stitches. you can add extra depth to your rows between motif blocks or you could just let it play out and not stress yourself. just add another set of blocks to the length of the blanket (i thought that mine would be a 3x3 square and it in the light of reality became a 3x4 rectangle and i like it all the better for it).
i hope this helps.. its a tad late/early