Sweats

You grab a shirt from your dresser and throw it on. This way you'll have something to cover you as you dash between rooms. It barely fits your petite frame, leaving one shoulder exposed.

Peeking out of your room you make sure the coast is clear before stealthily as possible making it to your sister's room, which you do so safely.

Immediately you dive into her closet, knowing exactly what you are looking for: the biggest, baggiest sweatpants and sweatshirt you can find to hide your new body as much as possible. It took some rummaging, but you found what you were looking for, and in just a few seconds you resembled a big grey blob.

Not wanting to be caught in your sister's room, you begin to make your way to the door, but as soon as you reach it you realize you don't have any underwear and you dash to the dresser, throwing open the drawers until you see them, various colors and shapes of underwear. Just as you grab a pair there's a clatter or sound.