I've never done a fast on only green tea. I've done a couple of juice and water fast, but not just green tea. I think it would still provide you with the benefits of a cleansing fast, so I don't think you have anything to worry about there.
Is this your first fast? I remember when I did my first fast, I was incredibly hungry for the majority of the duration. Right when I started to get used to the hunger, the fast was over... Stay strong. You'll feel better soon.