This quilt is oh so cute. But I do think you need some horizontal quilting lines. Batting reccomendation of 10" means 10" in all directions and it looks like you have unquilted space from the top to the bottom that exceeds that. In addition to the possibility of the batting migrating with long expanses of unquilted areas (in this case from top to bottom) it can also lead to some unsightly wrinkling of the fabric after washing. And undo stress on the quilt. I think you can follow your seam line and just stitch straight across and it will still look very cute as well as reinforcing the quilt. Should only take you an hour or so if even that.