Context, dear boy. What is the context?
The first meaning can hold if the context is:
"what were you doing when you were supposed to do something else"
or
"what [bad] things you just did"
or
"what do we do", among other contexts.
e.g. "I just said that he was a failure, not that he was a [insert curse word].", "You just need to keep up the good work".
The second meaning can hold if the context is "what happened in a recent timeframe".
e.g. "We just lost the football game!", "They just stole my car!"