When you try to drag the colored circle into a shape and the paint spills all over your canvas there are a couple of things that could be going on.

• The shape you are trying to fill isn’t closed, when there is a little gap the paint will spill out. Make sure to zoom in, but also out, to check your entire shape
• Your Color Drop Threshold is too low, when you drag in a color hold your pen inside the shape and start dragging it to the left or right. This way you can adjust your Color Drop Threshold and change the amount of paint that will spill
• Another layer is set to reference, make sure that none of your other layers are set to reference. You can check this in the layer menu

You will also find this video below helpful if you are experiencing issues dropping colors into shapes.