The gage you are using says it only measures when there is flow. Obviously once you shut off the valve no flow. The real test is if it will hold preasure.
Turn all of your appliances to off. Turn the valve off and then wait about 10 minutes. Go to the stove and hold a lighter next to one of the burners and then turn it on. OK this does best with two people. What should happen is that the burner will light
and then quickly peter out. But it should light
. If it doesn't then you have a problem. And as someone here has said, unless you are a really good handy man this is a job for the experts.
If that works then try opening the valve and lighting
the stove again and then turning the stove off. Then wait a hour and do the same test. You should get the same result.
That will tell you might more than that meter would.