A nether portal is a manufactured structure that acts as a gateway between the Overworld and the Nether dimensions. That diorama has a multiple things around it. You can put that things in position that you want. I prefer to put the mushroom in the right place, but no judgdements if you not want.
More About Nether Portal: https://minecraft.fandom.com/wiki/Nether_portal
1. Click on the papercraft design image.
2. Make sure it has not been resized by your browser (you might need to click the image again).
3. Print using your browser's Print function.