I can't get a blood moon.
I have Topazes and the Ruthless War Axe of the Night, and so I am ready for it.
Am I doing anything wrong?
A blood moon has a 9.72% chance of occuring when someone on your world has at least 120 health and the moon is not a new moon. I don't know where you've got the idea of topaz and War Axe of the Night from.
If you already have 120 health or above, all you have to do is wait.
Source: Terraria Wiki