Lemon Juice Fast... any suggestions?

Im going on a lemon juice fast because i have to lose as much weight as i possibly can in exactly 7 days for modeling and going to the beach with my boyfriend. I'm 5'8 and 15 years old and ive tried the veggie juice fast but got bored of it and wanted to try something new that actually tastes goood (at the moment im drinking it because im trying it out, although im starting it tomorow) Im just drinking a mixture of water, squeezed lemon, maple syrup, cayenne pepper and thats it. If anyone has any suggestions of how long i should do this for and what results i should be seeing soon and so forth. If you have any suggestions as to what exercise i should be soing and how long i should be fasting for just please let me know. Tell me if i fast for however many days, how much weight will i lose? Thanks!