Am i really as horrible as i think i am?

Im 14 and i am probably the nicest person you'll ever meet, i work hard, i get good grades, i understand, i ALWAYS consider others before me, and if theres a huge fire and someone's stuck i'll run back to save them, im a typical quiet teenager but i ALWAYS feel like i'm not good enough for everybody, when someone lets me down i take it as a normal thing because i tell myself that i'm the worst person in the world and i should be happy that someone would ever talk to me, i have respect for others all the time and i have really good manners and i am very polite but i think of me as crap, am i as horrible as i sound or am i just extremely sensetive inside, cause i overthink things WAYYYYYYYY too much but i just want to hear a strangers opinion