If you have had the paint for a while you should be able to take it back to the store and have it shaken which will probably save it or you can stir it yourself but it will take a while if the paint has separated. Most paint lasts quite a while. However your vanity will probably need to be sanded and you will need to start over once the paint has been thoroughly remixed.

Just dipping your brush in the can several times should have stired it up if it was freshj paint you just purchased. At this point why worry once the paint is dry you can look at it and see if it looks good or not.

I painted my vanity today with some clay and mineral paint that doesn't need to be primed, but I didn't stir, or shake it before hand. I painted over half the vanity after sanding those parts. My question is, is the paint ruined? It was a $40 paint and I really don't want to buy another can just because of one tiny damn mistake. Although, if I have to just repaint the vanity then that's fine. I just don't want to buy another can of that paint.