Your shallow well pump has a pressure switch with an START pressure (low) and a STOP pressure (high). You should shut off your pump, drain the water from the tank until it stops running, and then pressurize the tank to 2 or 3 psi LESS than the START (low) pressure.
You need to be sure that your air and water gauges are calibrated THE SAME or that you make allowances for that. It is absolutely essential that the air-at-empty be LESS than the pressure switch START pressure.