Using a spokeshave takes practice but the trick is to angle the blade and pull or push with a slight skewing action rather than simply have the blade shave straight down the middle. When the blade begins to chatter across the wood, I alter the angle or direction
and try the area again. With practice the tool becomes an easy way to delicately shave off wood and shape the paddle blade with finesse.
Don't have photos for this, but using a pair of spring calipers set to 3/8 inches, I routinely measure the blade's thickness from the tip to the 2/3rds guideline previously marked on the paddle's edges until it's been shaved down to this measurement.
Beginning to shape with spokeshave
Shaving down to the shaded edge guidelines
Blade shaped to 3/8 inches thick
Pile of shavings from the completed blade