Do I have to pay for Mountain Lion twice?

[bedouin]

I have been on my newer iMac and logged into my one and only iTunes account and it does not show up in purchased and when I go to ML it still says "Buy App". I did not click it as I did not want to buy it again and I can not remember if there was another step after you click Buy It.

Maybe after I click Buy It, it will give me another option????