I have an old Badger air brush set with a small compressor. It all seems to work well even though there is no way to regulate the air pressure. I'm wanting to spray a camouflage finish on a plane I've been working on. I did some test sprays and I like the way I can shape the pattern but no matter what I did I found small paint spatters outside the painted area. What have I done wrong?

1. Improper mix of paint and thinner?
2. Lack of adjustable air pressure?
3. Dumb operator?
4. All of the above?

I searched for some frisket to make the pattern but the only one I found would not stay adhered to the plane.

Any advice is appreciated. Thanks in advance.