Don't despair, if you have the cash, treat yourself to a square ruler the size you mostly make your blocks, it makes it so much easier. And using corner stones really does make a difference, though with these narrow sashings, that wouldn't be very visually satisfying. When the blocks are all the same size, then pin the sashings at the 'crossing points' and at at least three more places in each block, until you are managing to get them together more to your liking. Also, if you have a walking foot, use that too, it will help a lot.
Lastly, keep trying, as your blocks are really nice. Those planes turned out a treat.