Since you're so concerned you obviously don't deserve any of these harsh words Even though you've thought of the dishonest route a person who was so much less moral wouldn't care at all yet even then that wouldn't make them so terrible.

Would you try being truthful as to why you didn't go to the session anyways? Your boss should be able to see that honesty triumphs being dishonest, considering this is the workplace after all - some actually respect this when they recognize it. I can understand if the situation isn't as simple as I'm making it to be either, considering I don't know the whole story.