Hi guys if it will help I found that the maximum size in your logos would be 120 high and 150 in width. I never make mine higher than 120 because of the way the material stretches it distorts your little logo (picture). Also if its wider than 150 then it tends to curl around your babies waist. Also as mentioned in the tutorial the best position is usually if you place the mouse pointer exactly in the center of your image at 140 by 500. It does appear to be off center on your outfit when you make it, but the way the outfit stretches in game makes it appear in the center on the outfit in game.
I hope this little tip helps you guys out too <3