What does 上 mean as in 抱歉我没帮上忙?
上 denotes this sense: 


  （用在动词后， 表示动作的结果）(Used after a verb to indicate its result)  E.g. 穿上外衣; 考上大学


我没帮上忙 means (the result is that) I have been being helpless.. It's not a word for word translation though.