Make it less bended. And if you make it bolder, you can achieve more volume after baking it to diffuse, etc. Sorry for english, hope its clear what I wanted to say.
I already have vertex colors, but it's a good idea to make the transition less hard (fixed below). As for the sand, the materials are PBR so I'm not sure what I can do about the concrete look. Any ideas? Also the material is already pretty crazy so I can't actually add more displacement since the beach stones already are…