Ami has a great product that you can use for making your stencils and it's on sale right now on her website. It's called "Sticky Plastic."
Peel back the release paper to reveal the sticky side of this clear, rigid template material. Stick your original paper pattern onto the sticky plastic. Replace the release pattern and cut out the template with a regular pair of scissors. You're looking at the original as you cut, so you know it's accurate. Sold in 8.5" x 11" sheets.
By using your original pattern, you'll have a more accurate template.