When Creon asks Antigone for an explanation of her crime, she answers with the passage that begins on line 487 and ends on line 508 and starts with "I did. It wasn't Zeus . . . ." What is Antigone trying to say with this explanation?

Antigone boldly tells Creon that she is the one who dared to defy his law and bury her brother, Polynices. She knew that Creon decreed that no one should bury Polynices because of the rebellion he lead. However, Antigone claims that it is a heavenly law that the dead have to be buried. By burying her brother, Antigone is loyal to her family and showing respect to the gods. Although she knew the law that Creon passed and the consequences for disobeying it, she attempted to bury Polynices twice.
Antigone knows that the penalty for breaking this law is death. However, she explains that if a person is alive and has evil everywhere around her, it is better to die. She explains that her brother being left unburied brought her grief, but now she is at peace. She ends by warning Creon that although he calls her a fool for her actions, he himself is acting foolishly by going against the gods.
Antigone's response calls into question some of the main themes of the play about loyalty and the tension between moral/religious laws and the laws of mankind. Creon has made a public decree, and his pride and his belief in public order makes him cling to this, even in the face of Antigone's defiance. Antigone believes she is owed the religious rights and private family rights of burying her brother.

Antigone is openly admitting that she has defied Creon by burying the body of her brother Polyneices; she takes complete responsibility for what she has done. She further justifies her actions by telling Creon in no uncertain terms that there is a moral law we all should follow, a higher law than the laws made by men on earth. In so blatantly defying Creon, Antigone is following the law of the gods, not men. The gods' law is ultimately the one that matters; it existed long before humans first appeared on the earth and will still be there for all eternity after we've all gone. Creon, as a mere mortal, is showing hubris, or overweening pride, in defying the gods and refusing to allow Polyneices's body to be buried. He has made his choice, the wrong choice by Antigone's high moral standards. But Antigone has made hers, and she is ready to face the consequences of her actions.