I too once killed a second bird. Had 3 birds come in, all cookie cutter same size, so I just waited until one was clearly away from the other two. They had been gobbling like crazy and I was kind of sitting down very slightly below them. I shot and the other 2 buggered off and because my feet were kind of uphill I had to turn away to stand up. As I trotted out (I was a good bit younger) I saw my bird flopping 30 yards past where I thought he was in some thick briars. As I ran to him I saw the bird that I was actually shooting at in a little bowl. There had been a fourth gobbler that had come in and stayed in the thick brush that I never saw. (It was not illegal, I was on private and that was the first year you could kill 2 on private)
I passed a couple years ago on one and my son-in-law was mad at me, said I could have killed it. We paced it off and he was at 43 yards. I was using a newish 20 gauge and was not comfortable at that range (40 yards) and had said I wanted one at 35 to be comfortable. I shot later at a target at 43 and the pattern was good, but I was not sure at that point and so hopefully taught him a lesson on restraint.
About 2 days later, we called in a hard gobbling jake on my side and he said shoot. I said no thanks, you can kill him (he had only killed two birds in his life at that point) and he did. He kept saying sorry and I kept telling him I was not killing jakes at this place but that he had only killed a few birds and there was nothing wrong with it. It tagged him out for the year, but I got a gobbler a week or two later.
I have passed on several shots a little too thick, a little too far or a little too close together for my liking and never regretted any of them.
Don't lose your mind and you will be fine. It ain't about the shot or the kill, the real challenge is putting yourself in the position to take the shot and if you accomplish that, you won the game. If you pass because it is not right, you still won, your prize just may be later.