How do I get a punchy acrylic paint colour?
Henry is close, but the problem is that your acrylic is drying Matte. This is also, by the way, a problem with many different kinds of paint, whether they are spray paint, oil paint or acrylic. 

You can add glossy mediums to the paint, but I have found that painting a varnish (or firnis) on top generally yields more even results. I prefer sennelier gloss UV-protecting acrylic finish, which you can buy at pretty much any art supply store.

It really works!

The best thing to use is not any kind of spray, you want a thick, viscous medium. NEVER thin it with water, work from the center outwards and use a very soft wide brush. Don’t rework the gloss after you have spread it out, and be careful that your brush doesn’t lose any hairs.