you are not getting enough material on, its "dry", you want a wetter coat , slow down , you want a wet coat to follow the gun, this is a common error made in spraying , folks get scared of runs, so they spray to light , the trick is how wet to avoid runs , but wet enough to flow out level, try this , take a scrap , brush a "wet coat", that is what you want to replicate when spraying , I have often said if your not getting a run every now and again , your not getting it wet enough , you might also try thinning it a bit ( 5 to 10%), I always have a good synthetic brush handy , if I happen to get a run a quick brushing will level it out , if it starts to "set up" on you , wet the brush with some water , the issue you are having is you don't have enough material on to flow together , a sprayed finish is simply zillions of droplets of finish that flow together to form a film, too little material, you get a rough pebbly finish , too much you get a run, it definitely requires some practice … You will get it , but keep the brush handy , I been spraying since I was 13 , I'm now 56 , I still keep a brush around , Water base is tough to get the hang of , it requires a thicker film to level out , and its a fine balance , also be sure you keep the gun parallel to the surface , don't swing it in arch's , you want approx a 6" fan pattern, and be about 6 to 8" away from the surface …