I just gave blood and my arm is severly bruised. im only 16.?

so wednesday at school there was a blood drive. it is now saturday. it was my first time giving blood and im a small girl. i weigh 110 pounds and i gave blood in 7 1/2 minutes. i ped out later that day in school. but now my arm is severely bruised and its like my whole arm. im thinking a vein might of got ruptured but i have no idea. it was only a small bruise the day after. now its huge. i dont know whats wrong. and if it gets worse i might go to the docter. any help please?