After you have sewed the patches your block should look like this. See how it is nice and square and everything matches because you have taken care to mark your centers. If one side is a bit bigger than the other, rip it out and see what went wrong and redo.
After you have sewed all the patches on for the block, I personally do not trim, I block it. I spray starch it and pin onto my block pad where I have drawn my 12.5 square and I even use steam to block. I use an up and down motion, never slide the iron.
Here are 13 blocks, remember this is not the way it will set up. The star blocks will go between. Remember the original six blocks I made yesterday? I ripped of the last tri's and changed them to more flowery ones to create a more happy and light mood. Too much blue in those blocks made it seem too cold to me. Look at the block on right, the second one down, see that flowery arm, I love that.
The next three pics are of the block with the tri's matching to make the square, the blocking and then the 12 blocks on the board.