Yes!

You lean over and silently loop the handcuffs around the top of the metal bed frame before loosely closing the cuffs around both her wrists, being careful not to close them fully yet. You take one last look at Gwen's peaceful face and swallow nervously. With one cuff in either hand, and your heart in your throat, you squeeze them shut, the forceful clicking of the ratchet finally being enough to wake your big sister.

"Hmmm... huh?" she moves to scratch her belly, only to learn she now can't. With her arms now bound above her head, she can't even cover herself. Success!

"H-hey, what's the big idea?!" she angrily asks, cuffs rattling.

"I'm sorry Gwen..." you apologise "I can't risk it." You're now straddling Gwen as you watch her struggle to get free, and watch her expression shift from surprise to anger to mild fear as she realises her situation.

"I-is this about what happened in the shower this morning?" she nervously asks "Because I'm so, so sorry... I was still getting used to my new body and with all the new feelings and pleasure I just couldn't control myself-ah!"

She gasps as you ignore her and pull down her boxers. Her cock springs free nearly fully erect. Your thinking is that now with the situation under control you'd best... neutralise her.