aslam o alaikum!! Today I went to shop to buy something to eat. I went to a worker and she gave me a slip on which it was written that what I had to buy and I also gave her the required money. Then I went to the other ones to get that thing but inspite of asking it again and again no one listened. a girl who was standing nearby said me to take that thing and place the slip here. I did so and ate it. Had i done anything wrong? if yes what should I do? but I also paid the money to the worker

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

It is apparent from the question that the way the customer gets his order is by taking it directly and leaving the receipt as you were instructed by the girl. If this is the case, then there is no harm in what you did if you had taken your order and you did not take anything else, and your question implies that this is what happened.

Allaah Knows best.