I think this is an interesting start, but I wish you varied the sizes and colours of each sunflower a bit and added shadows (the bottom of the sunflower would be darker than the top). Also, rotating each sunflower helps so that the entire wallpaper isn't so uniform. Ideally, each sunflower should also be vectored individually and are at slightly different angles.
It's a good start, but there are some things you might want to consider for your future works. :)