I see by your other post that you are using a Badger 250. A smooth coat with this model takes some practice. It has a fairly coarse spray, so you can't just mist it on as you might with a better airbrush. It's more like using a spray can. And, it works better with a pressure of 25 to 30psi. Before you continue with your kit, I suggest you invest $3 in another bottle of paint and practice on some scrap plastic, like empty bottles. Experiment with nozzle adjustment, distance, thinning, and how fast you move until you get the knack of how to get smooth coverage. As others have said, you probably need to thin more. Try as much as 50:50.
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Don