What Went Wrong
I put the sky on first [cerulean blue] wetted the paper first then added the blue.
Then put the sea on Prussian blue mixed with yellow ochre but the sky hadn’t dried completely particularly on the left, hence the bumpy horizon.
The sand is a yellow ochre wash [very dilute paint] the people are painted on in thicker yellow ochre, the clothes and hair added when they are dry, quite soon in direct sun.
As an example of a different way of doing this, here is one I did last year on Ramsgate Sands, drawing the picture with india ink first [Pitt pen size S] and then painting it after