Stencil on wood issue
A combination of getting the right consistency of the paint for the stenciling and technique in the application should stop the fuzziness.

You would want a fairly "dry" paint thickness so it does not run when applied, more like paste than water. Keep the brush loaded with paint so you do not have to work repeatedly over the same areas but do not overload the brush with excess paint that will gum up and bleed under the stencil.

Then use careful light dabbing, possibly holding the stencil close to the surface with your fingers like Willeke said, moving in from edge to center to keep from lifting the stencils as you work. You should not need to glue down the stencils, but maybe use a little masking tape on the outer edges to keep them aligned.