I think that it's just a visual glitch. I've seen it happen too, and I don't think there's a way to fix it. You just kind of have to deal with it or redo the paths, but I think it'll show up in other places as well. It's more evident with yours' since your path is that bright white color. It's a lot less evident with a darker, more complex pattern.
I get this as well. As long as you're using edges it's gonna show and, as SonatinaGena said; it becomes more evident since your pattern is so bright.
I believe it's actually the very bottom part of the edge that's showing up looking as a seam. Almost like the patterns are off by a third of a pixel if that makes any sense to you.
I erased most of it and went with white flowers. I also took SonatinaGena's advice and darkened the walkway ( which looks nice in contrast to the white. ) I'll just have to figure out what to do with the area around the pond... ah well that's why they call it a WIP.