I would not press the lap button. On the 520 I believe the test is controlled via a workout. Pressing the lap button will cause the current step to be terminated and will advance you to the next step. This should happen automatically unless the step has been defined to continue until a lap press.
See what happens at the end of the first step. If it does not advance to the next step or tells you to press "Lap" when complete then use the lap button.