GMSH, i'm confuse how to setting the mesh density and shape
 

I want to make a hexagonal mesh like colored picture below (my reference). But confuse, some of my mesh just abstracted when i press "2D". I already transfinite all the curve but still abstracted. I just learn GMSH this week and don't know where to learn GMSH properly. Anybody know how to make my mesh good? Or some advice for me?