Id cap the gas line to your fireplace, at once , or find the shutoff
valve for the gas line feeding your fireplace and close it asap. Get
it fixed by a contractor familiar with gas fireplaces if possible.
Yes, if you shut off the gas meter ... you will have to purge air out of
all the gas lines feeding all gas appliances, water heater, furnace,
etc...before they will work. Let the contractor do that also.