For round 2 of the rose, we'll add the first round of petals. There are 6 petals, one for each loop of the previous round. Each petal begins and ends with a sc. There are dc's in the middle of the petals.
A dc is twice the height of a sc. And so, for a smoother curve to the petal, it would be nice to have a stitch that is about halfway in height between the two. That stitch is the half double crochet. At the right is a description of the stitch from the American Thread Company booklet. It's called a short double crochet there. (The British call the stitch a half triple crochet.)
To work the stitch, start out as if making a double crochet. But, instead of pulling the thread through 2 loops twice (as for a dc), pull the thread through all 3 loops. NexStitch has a video.
The second round is (paraphrasing the directions from the booklet):
2nd Row: In each loop work 1 sc, 1 hdc, 3 dc, 1 hdc, 1 sc.
Here are 4 petals plus part of a 5th. Since the pattern calls for 7 sts in each ch 3 loop, there is apt to be crowding. Scoot the sts over a bit to make more room for the rest of the sts. That's what needs to be done in the picture to finish the 5th petal.