The spell definitely worked

It takes several minutes for Siora to catch her breath. When she finally does, she returns your embrace briefly before sitting up. When she does, she turns to you excitedly. "It worked!" she exclaims, gesturing to her crotch. "I still have a penis, it worked!"

You look back at her with a confused look, prompting her to explain it more fully. "With just the basic spell, my penis would have disappeared right after my orgasm. I still have it, that means it worked!" She clasps both of your hands in hers. "I can feel it, magic from both of us, mingling as one. Can't you?"

"I felt it the moment you came inside me," you return with a smile.

When you mention her filling you, Siora looks down your body. "Oh my, the chain!" she exclaims as she takes one of your now freed nipples in each hand. "The stories about this ritual must have been true if it was powerful enough to break that curse you were under." You can only nod enthusiastically in response.

She continues looking lower, now placing one of her hands on your abdomen, just below your belly button. To your surprise, you see a mark inscribed on your skin, just above your crotch. It is in a stylized heart shape, with elvish runes in the center. "What is that!?" you shout in surprise.

"It is my mark," Siora explains. "My penis is my symbol of the spell that binds us together, this is yours. You see this," she runs her fingers across the runes in the center of the design. "This is my name in ancient elvish script. It ties your soul to mine."

"Then I will wear it with pride," you reply, pulling Siora into another embrace. "The eternal symbol of our connection."