I would not say anything to the giver.  He gave what he thought was appropriate according to the rules/social expectations that he was aware of.  

I would apologize to the receiver,  telling them something along the lines of "I made a mistake in planning and have learned a valuable lesson, that next time I will be sure to set a maximum and minimum amount."  


If the receiver continues to complain just repeat "I'm sorry I'll make sure it doesn't happen in the future."  

Good luck