So you blew the surprise party by mentioning it in passing to the birthday girl. Now, you have to do something to make amends, or reparations, to the boyfriend who worked all day to set up the party.
When you make amends, you mend something you have damaged, like a deal, or relationship. Maybe, your cupcake shop was panned by a food critic in the paper, but he never went to your store, he went to that awful cupcake shop across the street. The critic should make amends by printing a retraction.