Quiltervention!

Guys, I need a quiltervention!  I thought I was getting pretty good at quilting!  So I decided to test my skills to see if I was good enough to start on my dream Modern Crosses quilt.  You remember, this one:

I tried to make a practice square using some fabric leftover from The Hat.  It didn't turn out so great.  My square is not square!

Any tips?  I wonder if it's just a matter of practice.  I have only been sewing for a few months.  Oh well. I'll try again soon.... maybe listening to this song will help?  (Are "Intervention" jokes allowed???)