Children's train bookmark

My 7-year-old son just started reading his first chapter book, so he wanted a nice new bookmark. I told him to design something and I would print one out for him (his drawing can be seen in the images above). I've tried to thicken the walls as much as I could without badly distorting the image, but it is still quite thin, so this needs to be printed slowly. I printed the flat bookmark part at normal speed and then printed the train itself at 30%. It worked pretty well for the most part, but