HOW DO I GAIN BODY FAT AND WEIGHT AROUND MY BUST LINE AND WAIST, ONLY GOT ONE MONTH AND.PLZHELP!?

hi, i really need help and really good advice. Kso Graduation is just around the corner, and i got my dress and everything and its really nice and i wore it and it looks good cuz i gt curves and a hour glass figure but i really really need to gain weight and body fat around my bust line and waist. im 13 and around 90 pounds and im super tall i dont know exactly hpw tall but i think around 6ft 5? but ye im really tall, and i have a very petite waist and my bra size is 34A, so ye im pree flat chested . BUT REALLY REALLY NEED TO GAIN BODY FAT AROUND MY BUST LINE AND WAIST AND NEED TO GAIN WEIGHT!! SO PLZ PLZ PLZ HELP ON HOW I CAN DO DAT IN THE BEST POSSIBLE WAY, I ONLY GOT A MONTH!!! PLZ AND THANK YOU, IT WILL BE GREATLY APPRECIATED!