You fill up John's tank, fully aware of the consequences. Long hair flows past your narrow shoulders as your shirt becomes a white tank top. You feel your new breasts held in place by a bra as a small necklace wraps around your neck. Your jeans become tight as your legs become toned and slender, your hips and ass bulge out as you become a woman.
John comes out of the gas station but the effects of your wish mean that you know you transformed but he is unaware.