Hey, ease up on yourself. Are you trying to do this perfectly? That's a trap that many fall into with diet changes. There's no need, and the stress you put yourself through with it is worse than the stuff you're cutting out. If you're feeling overwhelmed with the changes you're trying to make, slow down. It doesn't matter if you have a little additives or sugar, especially if you run into a situation like you did at work. It's unavoidable. Sometimes dietary changes have to be made slowly. Whatever "eating right" for you is, it's unique for you and your life right now. And your body and your feelings are as much or more important a source of information about what that is as what somebody else tells you. So take in outside information, but listen to your body.
I don't know if this will help, but you might have a look. I find it to be a good reminder to be easy with this stuff: