You’ll probably need to refine the auto-trace settings to get it to match your footage closely. It’s probably picking up edge pixels off the bluescreen key (a tighter/more accurate key would also help). Try upping the tolerance and threshold values a little. Usually I have to experiment- try some settings, scrub the timeline to see how the mask looks, undo, try again.
As for the scribble, try playing with the Stroke Options in the Scribble effect. You should be able to get the look you want from there. It does tend to be a little jaggy, so you might want to move the scribbled mask to it’s own layer, then apply a very slight blur or glow to smooth out the edges.