This portal block is able to be printed out the same EXACT size of other blocks (mainly for obsidian, any block from the block generator will work also). Other portal blocks seem to be larger than blocks from the block generator, and sometimes, have a lower image quality. :)
Click on the papercraft design image.
Make sure it has not been resized by your browser (you might need to click the image again).
Print using your browser's Print function.