We were able to print out the original full-scale image from FIRST on our big plotter - a piece of cake and I highly recommend it if your team has access to a plotter.
If you don’t have access to a plotter, a couple other ways to make the target include…
Paint - white background, black circular band with sharp edges.
Bulletin board - white paper with a black circular band. Be sure to adhere the black all the way around, perhaps with rubber cement or other adhesive to avoid shadows.
Clingy plastic - purchase black vinyl at the fabric store, cut the black band and slap it on a dry erase white board. Shiny, but if it works there, it will certainly work on an official field. Very portable too.