A strip stick would probably help:
http://thestripstick.com/ .
You may also want to "block" the finished blocks. In other words, draw the finished size on your ironing surface (you can draw it on freezer paper with a Sharpie permanent marker and then iron the freezer paper to the ironing board). When your block is ready, spray starch the block and pin to fit the drawn measurements, then iron the block dry. Sharon Schamber has some videos on Youtube where she demonstrates how to do this:
http://www.youtube.com/watch?v=v-3RIWhBvcA
http://www.youtube.com/watch?v=sQkF02vpVuw