Do you have ammonia, and Nitrite test kits? You'll need them very soon. It looks like your doing a fish in cycle, so you will need to test for ammonia daily, and keep it at 1 PPM or less. Less preferably. The ammonia will spike, the fall, then the nitrite will do the same. Both chemicals are harmful to fish, and need to be kept at a minimum through multiple water changes.
In my opinion, it would be better to take the fish back, and go with a fishless cycle. Just my thoughts.