How do I handle being underpaid by a friend?

I was dog sitting for a friend and I would go to his house twice a day. Previously I took care of his dog once a day for $15. Usually I charge per visit. When we discussed payment all that was said was "Should we do the last payment as last time?" And I'm guessing he took it as per day instead of as per visit. Per visit it should have come out to $75 (5 visits) but per day it came out to be $45 (three days). I am not sure how to approach this situation because while he was away he also got me a gift (which he left in San Antonio but ordered another one) and he is a really good friend of mine. Do I tell him that there was a miscommunication? Thank y'all so much.