#1 Take it back.
#2 Get a refund.
Goniopora don't do so well in captivity. Most of the people that have had one grow (not just waste away over 2-3 years) are very experienced and admit to being quite lucky. Seriously, you've just bought an invertabrate mandarin.
If you insist on keeping it, you may want a bit more light, so you can put it in the sand on the bottom of your tank. They like to be fed, they like their water rather clean, but not pristine, and they like low speed alternating high flow. But seriously, take it back.