When you draw your tile, you blend with each side that doesn't have the black and gray checkered section that you see in the right hand corner of the tile you received. You started off with a four sided tile. I'd recommend refreshing the page until you get a tile that has the black and gray checkers on two or three sides so you can practice without having to blend all around you. Also, you will want to make sure your piece of art is exactly the size printed on the tile and aligned properly within the section, to ensure that there arn't any black lines.

Hope this helps.