How can I lose a lot of weight by June 13th?

Hey guys. I'm 15 years old and I weigh close to 195 lbs. I'm 5'5ish. I know... I'm overweight. I've tried everything though! I went to the gym for like 2 weeks straight for like an hour - two hours and I lost no weight. I need to get slim by June 13th because my school is going on a trip to a water park and i need to be able to wear a bikini! I really do not look like 200lbs though. I look smaller than that. I don't really care about getting my weight down, I just want to look good. I also cannot go out and but any dietary pills because my mom won't let me. I can however buy like drink mixes and stuff like that. Thanks for any help!