Another path to take when dealing with an image that needs to be blown up to a much larger size,, is to use a projector to shine your image onto your work piece and then outline it with a pencil. I took a few extra classes at work and some were art classes,, the instructor showed us several methods that they use to get large images onto surfaces,, I never would have thought of that before, but the projector method works great. The projector I bought cost me about $150.00 ( called an Opaque projector ) and you just set it on top of a picture of your image and it shines it on what ever you point it at. You can even set it over something small, like say you want to make a sign with your favorite Hot Wheels car. and it will project its image up for you to outline. Another guy in there bought an over head projector like they used to use at schools,, he bought it on ebay for less then 20 bucks, but you have to copy your image on a clear sheet of plastic first.
Now if you do not do this often, then its not worth it to put a lot of money into a projector you will not use much, but on the other hand, if you do plan on doing this more,,, then you aught to think about it,, with that projector, there is no limit you can blow up the image you are going to work on. The instructor has used it to do whole sides of buildings.
It seems like every where I go,,,,,,,,,,,,,,,,,,,,,,,,, there I am...