Both you and the airline share a responsibility for ensuring that you do not exceed regulatory limits in this respect. However, that doesn't mitigate your responsibility. I am not sure I understand your concern. Were you prosecuted for this transgression? I would have thought (unless this was a recurring event) that was highly unlikely. You (and your employer) wouldn't be the first to commit this transgression.
How will it affect your future job prospects? I can't really see why it would even arise as an issue. A hiring company may check your logbook records particularly where the hours requirement is crucial, however I cannot see why they would audit each and every monthly total, unless there was something glaringly wrong.
I really do think you are worrying unnecessarily, unless there is something more to this?