Small waist fast help?

okay i think im a fat beast im 5'3 1/2 im 162 i have curves a lot people always say if i lost weight i would have the perfect body but i don't have fat legs and im not ugly just my waist is still curved but i have a stupid gut im 17 and im in to boys and i want to look as cute as possible you girl know how it is i use to weigh 140 and i was skinny but i don't have a double chin but im slightly getting a line and i need to loose that fast i just want a smaller waist and skin-yer face and a little bit slimmer arms but im really focused on the waist that's it and i keep trying diets but i always quit im so addicted to soda and i never work out i was gonna start doing sit ups 100 every night and just cut down my eating cause i need to loose at least 20 pound ill be more then happy 30 would be the best!! what about the corset i use to wear one every single day and when i first bought it it was so tight and then after a while it was to big but i don't know any help Lady's and guy what do you also think about my body gross huh