:/ If this was you being a perfections it would be one thing, but from how you describe it, it sounds like you're doing a very demanding job..
Personally I think that you should just try to do the best you can. That's all you can do. From what you said, it looks like you really tried. If they don't accept that.. well, perhaps it wasn't that good of a workplace, and firing someone because he hasn't done a 100% perfect job seems absurd to me