Zip purse frustration!

[to-my-wife.livejournal.com]

I've been trying to perfect my lined zip purse technique but no matter what I do I keep on running into the same problem. The end where the zip stop is looks lovely, but the end where the zip itself rests is puckered. I'm following this tutorial and I can't see where I'm going wrong - only both my ends don't end up as flat and pretty as hers, only one does!

Can anyone shed any light on what I might be doing wrong?