Anyone who has been to Atlantis, Bahamas should be able to answer this!!!!!!!!?

just a heads up... im going on this same cruise apr. 11, landing in nau apr 13 which is a tuesday. When i tried to buy this same atlantis excursion it was already sold out. I tried to book it last week. So it is possible for it to sell out, but i guess i did wait till the last minute to add it on (being spring break). So i wouldnt wait too long if you do decide you want to go to atlantis. So now i wonder if i can go directly to the park like you say and purchase them still, without going thru carnival to buy them.