One thing that no one seems to mention - not sure if it's because it's taken for granted or because no one knows about it!!
When you're doing a hem on a cat cut (or any curve) it's handy to clip the curve. If you've never done it - you make little nicks (I use my thread scissors every inch or inch and a half in the edge of the fabric. It relaxs the tightness of the edge and allows it to essentially stretch out to fit the tighter curve on the fold.
Try it with a piece of scrap first until you get the hang of it!!