Your FPR just keeps a set pressure difference between the fuel in the fuel rail, and the intake manifold pressure/vacuum. Constant pressure difference across the fuel injectors means that you can accurately control the fuel with the ECU.
So basically, your fuel pressure will only be 3 bar when the absolute pressure in your intake manifold is 1 bar (zero boost, wide open throttle in a n/a car). Average manifold vacuum at idle with stock cam(s) is 15"Hg, which is 0.5 bar vacuum. 3 bar FPR + (-0.5 bar manifold) = 2.5 bar referenced to atmosphere = 36.x psi.
If you've got a vacuum section on your boost gauge (if you've got one), what does it read?