Look at your stencil with magnifying glass and you will see that when the stencil dried, it shrank as the water left and took on the texture of the mesh. NOT a smooth hard sharp edge like you positive, but a dimpled ragged edge (sawtooth), because the mesh is effecting the stencil and there is no film on the surface of the mesh forming gasket to control the ink.
Pressure washer?
Covered, unexposed stencil will dissolve with water and rinse down the drain.
Detail has nothing to do with you water pressure compared to:
- Vacuum
- Single lamp vs. multiple lamps
- Penetration power of lamp
- UV output of lamp
- UV opacity of the positive
The time honored 'cheap' alternative is the car wash.