Looks like your blocks are all together, so if you haven't swirled your seams, it's a bit too late. You can give the centers a good shot of steam, hit it with a hammer a couple of times (against a wooden board, not your ironing board)
Or clap it:
http://www.youtube.com/watch?v=YsFy8wgHabQ
The trick to using a tailor's clapper is to use steam, apply pressure and keep the clapper in place until the fabric is cool.
Only other comment is if you haven't pre washed, the steam might shrink the fabric...