Don't worry about the gauge at idle, shows no boost, should be just sat in the negative section of the display, even when driving gently under small load the gauge will read between 0 and a minus figure when you come off the gas, it won't start showing boost till it reaches a designated point, usually anywhere betweek 2.5k and 3k depending on car size of turbo mods etc, gambit should be able to tell you roughly where your model starts too come on,
If you have a leak it won't hold boost at a steady pressure, you'd see it on the gauge by it not rising properly when giving it some welly, would probibaly get to a certian figure (we'll call it 0.5) then drop a bit and try again, if you have a leak chances are the cel light would indicate a problem, and put he car into safe mode before you did anything to destroy the car,
Could always get a odb reader and some software for your phone to check
Sent from my SM-T210