Yes, it would look very cool if the comic went to the very edge of the coaster. But, that actually won't work for this project. See, the edges of the comic book need something to affix onto. If they go all the way to the edge of the coaster, they won't have anything to stick onto. So they'll be floating in the air, basically. That makes it really easy for the paper to catch onto something and tear off and get ruined. So, you want to leave a little surface area around the comic so that the Mod Podge has something to glue it onto. If you're using an old coaster from the thrift store and don't actually want any of that showing, you can spray paint the old coaster before gluing the comic book onto it.