I don't know about 'work', but I imagine you feel good about handling things better this time. I recently read a quote "The only mistake you make is the one you don't learn from" - you're obviously learning, so these are opportunities to do things better, not screw ups \:\)

How about an email, saying that you're sorry your purchase casued a problem for him and asking if you can do anything to help with that - what was he trying to buy, lunch or something frivolous?

The bigger discussion about overall money management should definitely wait until no one is mad.