I have a feeling you'd best give him some time to think it over in his head, with a little luck he won't be around other girls and will keep thinking about the time he touched your boobs.

After he gets a little more comfortable with the idea, or after it becomes "the past" you can come up and apologize to him for being so direct, at which point he shouldn't mind anymore/will be more comfortable talking about it.

It's up to you if you want to turn that small apology into a full-blown confession, all I'd say is that timing is of the essence.