[prenaud]

I messed around with building something similar just before the holidays: https://steadyhand.app/

It was a blast to learn how to do things in canvas and as an exercise, a very fun little app to build. I'm not sure how the OP is measuring perfection of the circle, but in mine it was standard deviation of every drawn point around the centre of the page.

I encourage people to try to scaffold something like this together in canvas/JS sometime. Very fun project!