Thank you for the comments yesterday. I thought today I'd show you how I finished this off. Here's what it looked like when I left it...
...and this is what it looks like now... so what has changed?
I started by adding a little more stitch to the bottom and to the top right. I didn't want to completely feel the areas, but it felt somehow unbalanced as it was. Then, I took a blue coloured pencil and worked my way round the edges of what I finally worked out is an abstract mermaid. When that became clear, I then made a series of marks over the lilac with the same pencil, to suggest scales. If you click on the image, you should be able to see them. I've since gone over some of them again, to make them more obvious. I did contemplate stitch in some places, but felt it would be too much.
From the outset, I've had difficulty photographing this piece. This time, I've deliberately increased the tone to let you see that one of the results of drawing round the edges of the lilac, was to introduce some green. I knew the piece needed green, though it didn't seem to be logical or sensible. Using the pencil, produced green where it hit the yellow areas. It works.
So...is it finished? I'm not sure. But it is moving in the right direction, and I do feel a lot better about it. I'll keep you updated if I do decide to add more.