Leave the house immediately, without flipping any light switches or using anything electrical on your way out, since a spark is a real ignition risk in a gas-saturated space. Once you’re a safe distance away, call from outside, not from inside near the source. Don’t try to locate the leak yourself or turn valves on and off unless you already know exactly where the main shutoff is and can reach it without walking back through the affected area.
For a new installation, gas line and appliance connections require a permit and inspection, and we handle that as part of the job. A rotten-egg smell is the added mercaptan compound utilities put in naturally odorless gas specifically so a leak is noticeable, which is the whole reason to take that smell seriously the first time, not the second.