How many calories should i eat a day? maybe 800?

hi! i'm a 15 year old girl, 5'7, and i weigh 91-92 pounds. but i feel like my thighs are so disgusting and squishy, so i definitely want to lose some weight. i was supposed to start today, but i completely caved. ): i had a clementine, a 100 cal rice krispie, a 100 cal pack of chips, and a whole sandwich! plus like half a bowl of cereal for breakfast. but tomorrow i'm definitely cutting down. does 800 calories a day sound like a good goal? i want to lose like 10 pounds, but then keep going. that's just a starter goal. how quickly can i do this and how many calories a day would i have to eat to do it? THANKS!