Craig: that isn't your problem. The referee has the final say on all decision. I have been overruled as an AR on a penalty decision, and overruled an AR on one too. Yesterday, I was an AR on a match and flagged for a foul. Referee came over, I told him IMO it was a red card for DOGSO. Referee said that there was a covering defender the other side, went with a yellow.
End of the day, the referee should have overruled you - or at least had the conversation 'I thpught he got the ball, are you 110% sure?' 'No' 'OK, no penalty.'
Don't beat yourself up over another's error