HELP! Am i overweight for a 12 5ft1 girl ? Please Answer !(Anyone Answer)?

Today is fathers day and we took my dad out for breakfast and it was a buffet ..i ate alot.. well it wasnt as much as my dad ate but too me it was alot. After that we went to my Grandpas (And Grandmas) and i went to the bathroom.. after i came out i noticed a electric scale and i always see myself as a fat girl and i wanted to know how much i weighed and i got on the scale it read 76.8 lbs. What do you think am i overweight for my height and age !? :( And it was also after a big breakfast and 1 big glass of water but still i tihnk im fat :( Please Help i need your opion.. i dont like myself and i get upset alot.. i wish i was different :( im sorry for saying this stuff and it might make you mad some how but honestly i dont know anything about how much i should weigh and yea :( Im sorry but please Help me!:(