You should be able to win this race easily. You're usually a faster runner than Maddi, who is now weighed down with huge breasts and a huge--and unfamiliar--penis. There's only one problem.
Maddi with her huge breasts and penis is the most erotic thing you've ever seen. You hate the thought of winning the race and turning her back into an ordinary girl. You want her to fuck you right now. There's only one thing to do. With the finish line in sight, you fall down, clutching your knee as if you've twisted it. Maddi runs past you, and easily wins.
Maddi comes up to you with a big smile, watching the throes of your transformation into a girl with huge breasts and a high sex drive. "I knew you'd let me win." she says. You say nothing, as you are busy pulling down her pants in your quest for her magnificent new asset.