Another thing about carpet anemones is they can get very, very large and can be serial fish killers. A guy in my local reef club had his hand stung terribly by his carpet grown out of control, and the anemone had eaten several of his favorite fish.
I'm not coming down on you for your decision because it's your tank and nobody has a right to yell at you about it or get personal, but you asked for some advice. My advice would be to return the anemone solely on the basis of this fact:
It will ultimately die, probably sooner than later (but I've seen one live more than a week in sewer like conditions), because lighting is way too weak and your parameters aren't stable for it yet. When it dies, it can make an apocalyptic mess. I'm not just talking out of my hat; I knew someone who put a carpet in a 20 gallon tank with just one "reef rated" fluorescent light tube right out when he started and when it finally gave up the ghost the water turned to a nasty milk color.
So I'd return it just to avoid the hassle of a big mess when it dies.
