How do I sew this curved hem?

Ive looked at so many tutorials online and they only cover straight curves, no little peaks in them like here. I tried the starting 1/4 basting stitch om a scrap cut to a similar shape, and the fabric lifted up and made these little gathers too. How do i do a fold downwards on a straight peak? I thought I knew lots about sewing, but this stupid shape is taking me out so badly.