Hold the beveler straight up and down about a 16 or so of a inch off the leather start with tapping / hitting it and move the beveler a small amount each time and you will have a smooth bevel. Something as small as the shield i would just wet it like you did and wait till looks about dry and start working. When the moisture is just right the tool will leave a dark mark.
On you shield it looks like you set the beveler down each time and thats what made the tracks.