I can read French a little bit, but I can answer you only in English. It's a nice photo, but maybe the problem is the crooked horizon?
Apologies for answering in English, but my French isn't good enough to answer your question (perhaps Google Translate can help you out.
Even though the sky is starting to acquire some pretty coloring, about 3/4 of the frame of the image is very dark and a bit drab. In situations like this, you have a few choices. Wait a bit for the light to hit more of the sand, reframe to get mostly sky and very little sand or get out in the water so the sky's light is picked up by wet sand and the water over it. In all cases the goal is to fill more of the frame with interesting colors and textures, light and shadow.
I absolutely adore beaches before sunrise, so I've done many, many of them. Only a subset make good stock photos though Hope this helps
L'horizon n'est pas droit et il y a trop de plage, sinon les couleurs sont top.