Yes, you control yourself.

Until you get the nuances of how these are programmed, you decide to be passive.
"I will try not to, Abby," you say confidently.
"Your thing looks rather hard. When mine gets that way I often can't think of anything else," she presses.
"I have more experience, it won't happen again," you solemnly vow.
"Don't be so serious, Daddy! I'm not mad. Just do your best to keep from squirting me. We all know accidents can happen in this situation. We are after all male and female. Climb on in and turn the water on, we can't be here too long, or the others may get suspicious," Abby gestures for you to climb into her cleavage.
You put one foot between her massive mammeries that overflow the sides of the basin. You feel her balls part beneath those as your foot sinks down until you are straddling her breast. She puts her hands on your hips and gently tugs you over until you swing your other leg up and around into place and sink waist deep between her boobs.
"My...you sure are leaking, Daddy. You better turn that water on so I don't notice," she says with a sly smirk.
You reach over and turn the knobs until water cascades over you. Abby puts a bottle of body wash in your hand.
"Come on, give my boobies a good lather," she closes her eyes and smiles. "Your boner is really hard today, Daddy. I can feel you rubbing it on me. It's okay, I'm getting horny too. Just try to wash me quickly."
You lather up her expansive breasts as quickly as possible. You try to focus on the task at hand, rather than the well-endowed shemale you are standing in. You finish up the first breast and move on to the second, as if racing the clock. The problem is, the faster you go, the more her tit jiggles against you, massaging everything it is in contact with. You can see Abby feels it too. Her hands on your hips move lower and lower.
"Daddy, are you finished yet? I...I think," her cock unravels from around her neck as it stiffens, "...we are going to have one of those days!"
Abby heaves up from her sitting position. Her hands slide to your ass and keep you pressed into her. Her gargantuan cock swells to its full size.
"Alright, Daddy, you know what to do," Abby says as she looks up and eyes the tip of her cock several feet above her head. It drips precum into your hair.