In order to position my stencil correctly, I used paper masking tape and fixed it over my background. This is how it looked like before the first Marilyn was painted:
Then I painted it over. Of course the downside of this technique is that the stencil got stuck to the canvass (if you will not remove it quickly enough, you may damage it) and the additional “connecting” lines were leaving a trace on the painting. Have a look at this image:
Warhol used completely different technique called serial silkscreen printing. This technique is described with some images in this blog post. I researched it only after I was done with my painting, as I didn’t want to create a copy – only a painting in its own right. Here is the end result, please judge yourself if it was worth the trouble. For me, the answer is a definite yes. I hope that my friend will be happy with it.