The next step is felting. I used an embellisher to felt in the horizon with grey wool tops, then filled in around the rocks with white tops and a bit of grey in the centre. Finally I added some wisps of white for the wave in the midview.
Basically, all you are doing is using barbed needles to push the fibres of the wool into the backing fabric. The silk pieces will also felt into the backing, so go over them as well. The rainbow spun will not, so the more the silk and wool overlap the rainbow spun, the more stable you will make the rainbow spun. I use only tiny bits of wool at a time, and hold it in place where I want it with a bamboo skewer, which I remove once I have lowered the needles into the wool. I am no expert at felting, so if you need help, you will find some excellent tutorials here.
In fibre art, every scrap is the threshold of a new discovery.