It's not important whether the shot "could" or "might" have made it through or not...you were uncomfortable with a marginal shot and you chose to pass on it. Excellent choice. Very hard thing to do and you did it. It's history now and don't second guess yourself for leaning to the side of sportsmanship and respect for the game you hunt.
Consider the mental image of that healthy buck taking off as your first real trophy from the woods. Remember...that buck probably lived to pass those genes on to a few other nice deer.