It actually works pretty well and came together in about an hour. Check it out.
Step 1: Cutting up the cardboard
Thanks to the folks at this forum where I got the layout for the target area.
With the file handy, I cut all the pieces out on our Epilog laser cutter. I know, I know, you don't have one of your own, but with an X-acto you can cut everything up just fine. For the holes you can maybe use a drill.
Note: I attached eps and svg files so that they can be opened and edited in Illustrator or Inkscape. Since these files are not what I consider final, I am not providing a pdf.
Step 2: Assembling the ramp
For the ramp piece itself, I used an X-acto to slice lines across the back so that the front would have a smoother curve to it. After this was done I used the body of the X-acto as a guide for the curvature of the ramp.
Step 3: Target
I glued the two center pieces together first, keeping them at a right angle to each other. Then I glued the side pieces on one at a time. No real advice for this, just try and keep it even and you'll be fine.