Is your stitch length to tight? The bias will be on the edge and those can get wonky if you are not careful. I am starching my Spiderweb blocks and they have bias edges too. I mist and then iron while damp so that shouldn't matter. The good news on bias edges is, all the intersections will match because they streeeeetch. I will just quilt the heck out of my Spiderweb top to iron out any wonky-ness.
Hopefully someone who has made the same pattern will have some pointers for you.