Low confidence need hlp!?

im a frshman in high school, black, tall, smart and athletic. my point is im just not confident at all and i have a low self esteem. i always walk with my head down, i always think negative and i dont think i am very attractive to anybody. theres this cute girl my n my science cl that my friend thinks likes me, but i dont think she does. i like her but she doesnt know. but thats another thing.when i was younger other kids would tell me i was ugly and just put me down. but my family and even a couple of my friends and cute girls think im cute and handsome but i dont belive them. i lift weights, exercise, and play basketball but im not a confident basketball player either but evry1 says im good. i always put myself down mentally im a nice person and i dont act like i have low conf. & se.confidence to me is being able to go, say, do, anything w/o worrying wat ppl think & its knowin that i look good & dat i can have any girl i want cuz i look gud. i want 2 be able 2 think dat. plz help!