Quick stencils I made of the American flag. One is a positive image (stars are white), the other is the negative image (stars are black).

You're on your own figuring out the individual stars. My suggestion would be transfer to contact paper, spray adhesive on the stencil, tack it to the "canvas", remove tape, paint, scrape off the stencil.

Model is 5mm thick. Drop below bed to make it thinner.