Hello! Congratulations on your first set up, and what sounds like a great start to your beekeeping spring! Comb development is going vary depending on local climate, the amount of bees present in a hive, and sometimes just the genetic lead of the bees. The drawing of the comb seems appropriate, as the queen is likely is laying her brood on that center comb, with her bees clustered around her, thus the newer of the combs flanking the center one. We suggest continuing to monitor them in the coming 1-2 weeks, as if normal, you'll see a dramatic increase in comb building in advance of height of local nectar flows. When the bees start drawing their last 1-2 frames in the box, it might be smart to add that additional box to your beehive!