I'm starting to undercoat my car with U-POL Gravitex. I have 12 Bottles. I hope it's enough!

But i have a question. I've practiced a bit with the gun and i found that around 45psi and 15cm distance gives the right texture.
My problem is that when i spray the surface, everything looks really fine. But when it startst to dry it starts to get a matte finish and looks like the material starts loosing it's texture and flattens out. What did i do wrong? The problem is that i didn't see the original underseal texture on my '69 car, so i'm just guessing based on photos here in the forum.
My second question is that should i spray two layers? It looks to me, that if i spray the second layer an hour after the first, then the texture is more durable and doen't levels.
Any opinions?