And yet with the other choice you might have regretted "not having done everything you could have". That is the curse of those with the ability to actually do something. In many ways, those who do not understand and simply place their faith in doctors are less burdened.
You did what you thought best at the time; that is all you could have done. Nothing you did or did not do was a mistake.
There are no "right" answers when facing mortality. My sympathies for what you went through, and I hope you are doing better.