Using the rolled hem feet is not as easy to figure out as I had hoped. I messed around for an hour or so with them, trying to make a consistent, even hem, and came up with this (and this is the best). The piece of fabric had been cut perfectly square on my cutting mat.
The instructions that came with them are nearly useless. So this morning I went looking for an online tutorial. I found several, including a video tutorial, but the most useful one was here, at The Sewing Divas.
I looked at the pics, read through the instructions, looked at the pics again, and something clicked, and I realized what I'd been doing wrong all along (putting the pre-rolled hem at the start under the right side of the foot).