That middle flower is awesome!!! Beautiful work! It really looks 3D.
Okay. The stems...@snowbear might be better suited for a reply here, because I tend to struggle with this, too. But since you're not going for realism, I'm not convinced it matters all that much. Here, the visual impact of the flower is what grabs the eye.
But, I know what you're asking. It could look in better proportion if maybe the very top of the stem was less thin stem, and more pedicel. (Yes, I had to look that up.) The pedicel is the top part of the stem that widens out into a V-shape, and that thicker visual effect might be enough.
I've played with having stems come from the sides of the flower, too, to be able to add some length.
I'd look at a lot of photo references, too, for placement ideas. But again...it's not for realism! The gorgeous flower is the star.