Chalk paint Nightmare

I am trying to finish a puppet theater with rustoleum navy blue chalk paint. I have painted multiple coats and they seem to dry with darker patches on them. The top coat doesn't cover evenly to compensate for this. What could I be doing wrong?? I use a good Purdy brush. I started in my basement workshop. But then I thought maybe it was too chilly. So I moved into my craft area. But still the same thing. It dries patchy with some darker spots. What am I doing wrong???