What type of stencil are you using? I just got my personalizer plus, and have the same problem when using the paper stencils, because they won't stand the higher settings to mark the etch, if I use the sample stencil that came with it I can get the black to stay on, and looks good, with the paper stencils, it blackens all around the mark. If you have a good made stencil, you should be able to put in on the etch setting, and then switch it to mark and be good, also you may need more etchant on the applicator pad, not dripping wet, but damp, just guessing as I am still practicing with mine to get consistent results.
Dale