Remainder money that was collected for a function

I have a question regarding some money left unused post event. At a college function I and my class mates were organisers and we collected money from mates and juniors. The intention was clear that all money should be used, but some amount has been not used. So now who is the shari'ee owner of that money? Is it permissible for me to take back money which I had given for the event? My mates have an excuse that we were helping physically and fancially? Not the others. Do organisers have the right to take the money only what they have given or whole amount? If not what is the shar'ee hukum?