you're backsliding moose, the point is to get beyond wouldve couldve shouldve.
if you want an A+ then get one, and quit making excuses. But it is much, much harder to go from an A- to an A+ than to go from a C to a B or a D to a C, since in those latter cases any correct answer pulls you up, but in the former, you can't miss anything. It is quite wrong to think it was only a minor matter to get an A+, because you only missed one question. If you had focused on that question you might have missed two others. leon is right about carefulness, and focus.
but I still maintain it is not the most important thing to worry about. forget it, set a new goal, and move on to something that counts.