ARGHHHHHH!!!! and I don't mean that in a pirate sort of way! Although thinking of Johnny Depp briefly helps.
I first started working with the purple hexagons and used a 1/4 inch seam allowance which seemed like a very small amount of fabric to work with. I had a bit of trouble but thought they looked OK. Then when I tried to join them, I found they were kinda lopsided. After a bit of frustration, I decided too throw the lot back in the stash and work on another project.
After cooling down and not being one to just give up, I decided to try again this time with the blue hexagons. I used a more generous seam allowance but these too did not seem to match up. I thought maybe I could make them fit when I attached them. No such luck. Not only could I not get them joined evenly, the joining stitches were visible.
I think its time to step back and read some more tutorials. I must be missing something.