finishing it with the serged edge will prevent roll up, you might even consider a heavier decorative thread in the loopers such as YLI pearl crown . it makes a gorgeous finish. this is how I finish many items.

Thanks movingwest, I did try serging with regular thread and it still rolled up. I will try the decoritive thread idea it sounds beautiful. However, last night, I did finally figure it out. I tried cutting a ruffle with the knit running crosswise and a 3 inch hem but it didn't look right, too bulky. So I went back to the original ruffle with the knit running lengthwise and did 1/2 inch hem with 2 rows of stitching 1/4 inch a part and it seemed to stabilize the hem from rolling under.

that's why they use a coverstitch on so many knit hems. you discovered the magic.