In Florida, yes you can. If you truly feel your life is danger and you own your weapon legally, you can claim it was in self defense.
The question is if Zimmerman was the aggressor (which I think he was), does that still apply? That's basically one of the most important factors the jury has to decide.
There have been some cases down here where someone was getting their ass whooped and shot in self defense and was not even charged. But in those cases they clearly were not the aggressor.
I'll try to pull some of them up.
The defense is not arguing stand your ground. Which what apply to what I highlighted in the bold.
Zimmerman showed no sign of being beat to death. If he was getting beat to death, then he would've spent days in the hospital.