I've been known to use glue stick to ensure that my seams match, as well. It's also handy when my hands hurt too much to manipulate pins.
Also, check that you're cutting on a FLAT surface and that your cutting mat is flat as well. It's amazing what cutting on a flat surface can do for your accuracy.
For what it's worth, I'm doing a 5.5' flower square swap at guild and many of the members have been quilting for a very long time. I've learned that not all 5.5" squares are created equal. It's sort of liberating...