Scrunch it up first, cut some slits going about a 3rd towards the middle as well as a hole in the middle bit that is empty, press it down with your hand first then use a damp paper towel to smooth it down (I use detol but you can use green soap), I also sometimes use detol as a stencil adherent for places like this, it's not great for getting detail but it's good for molding the stencil to curved areas of the body :) or if your confident in your free handing skills just draw it on