After playing with Bloop a little more I can see that it's working, the inertia is just that extreme. I think toning it down a little bit might be a good idea since currently I feel hardly in control at all.
For the drawing, I don't think highlights will solve the issue. If I have a line basically "colored over" to the point it's not visible and it's not detected as drawn then a highlight will only tell me to re-scribble the same area over and over and count on luck. It kinda looks like there might be some bug with detection, since some lines disappear when you vaguely draw near them, and other are extremely persistent to the point where I had to resort to randomly scribbling nowhere near them to move on.
And since improving detection might be hard, a manual "move on" button would be a nice stopgap measure, and might even just be a temporary measure. Alternatively have it move after some time/some time spent without drawing or something like that.