Inside the box you just opened, you found that it contained a bunch of women's clothing, along with some women's underwear which were actually pairs of panties, and bras that looked like the perfect size for you to wear at the age you were at. Of course, the complicated part was putting on the bras.
You take a look at the side of the box, and see that it read "Used At Age 21". That was the age you were planning on entering your 3rd year of college with, but judging by how you now have the body of a woman, you will need all the help you could get. So once you've stripped out of the male clothes you were trying to put on, and fail at, you grab a pair of panties, and a bra. Both of them were black as you placed each piece on over your breasts, and privates to wear below your original clothes.