Not necessarily, under Florida law. Florida law significantly restricts the ability to use deadly force for people who commit a forcible felony (which, if Zimmerman had started the fight, he may have been doing) or provoke the use of force against themselves.
I read the FL statute much differently then you, then:
"...initially provokes the use of force against himself or herself, unless:
"(a) Such force is so great that the person reasonably believes that he or she is in imminent danger of death or great bodily harm and that he or she has exhausted every reasonable means to escape such danger other than the use of force which is likely to cause death or great bodily harm to the assailant; or
"(b) In good faith, the person withdraws from physical contact with the assailant and indicates clearly to the assailant that he or she desires to withdraw and terminate the use of force, but the assailant continues or resumes the use of force."
Even if I rob you at gunpoint, if you then gain the upper hand and begin beating me to death, and I can't get away, I am justified in using deadly force.
Both parties are restricted to proportionate force.
At least that's my interpretation.