Quilting SOS

I have been trying to crack on with my half square triangle quilt. Has anyone ever made one of these before? As a first attempt I am finding it to be incredibly frustrating! I spent a long time cutting out perfect 5" squares, only to find that when I had sewn them together and opened out the two sides the square was all wonky again. I have therefore had to trim them down to 4" squares and go back to the cutting board as I had nowhere near enough. Does anyone have any handy tips on how to avoid this, or is it just an inevitability? Thankfully I am not alone as my sister has been having similar difficulties, you can read about it here.

I have just cast my votes for the Blogger's Quilt Festival over at Amy's Creative Side. All of the quilts are gorgeous, some people are so talented!