The reading you see on the boost gauge when the car is idling is the manifold vacuum. If is - 0.4 kg/cm² or -400 mmHg, that's good. This is basically telling you how "tight" your engine is. -0.4 is good, -0.45 is better, but it's not critical.
I find strange that your car does not boost higher than 0.6 kg/mm. IIRC, it should be 0.9 - 1. If it doesnt read any higher, then either there is a leak or your turbo is not making enough boost. Does the car feel fast or not so fast?