I interpret this directly as: don’t ever put yourself in the position where you might regret the things you didn’t do,
which leads me indirectly to: don’t hold back from doing the things you could have done because you’re likely to regret it later.
The word adventure didn’t spring to mind when I read your post (though I get what you mean). Holding back from the things you could have done could be interpreted as just about anything, but it depends on context. Examples: you could have sent a letter; you could have taken a job; you could have helped a person in need. Or, it could be something more adventurous as: you could have taken that road trip; could have asked that person out on a date. In all instances, having taken the plunge, where might things have led had you said yes?
Your lines:
Go now, go now, don’t hesitate, your only master’s you,
Don’t ever let yourself regret the things you didn’t do
have great clarity. Fab!