I always do 3 chains w/ a dc unless told otherwise. Perhaps you are adding an extra stitch in too? maybe going one too far at the end? Looking at the rounds, they don't line up properly. I would bet it's because of the chain 2 instead of 3. Try it that way and see how it goes. There will be a bit of a seam but it really shouldn't be too obvious, esp if you're using a single color and not a muti-color yarn.