Honestly, in hatching the only scenario in which you can be SURE a death is your fault is when you assist too early, and it bleeds out or gets a ruptured yolk sac or something. Not being able to prevent something isn't exactly the same as causing the thing, so in hatching, unless you've done a botched too-early assist, you really, really can't blame yourself. There will be losses, and babies that hatch with problems, and you can't prevent it, and shouldn't beat yourself up about it. You just do the best with what you're handed, which is what you've done.