You didn't bed your pads. Light driving won't do it. You have to get the pads HOT so that you get a layer of the friction material on the rotor surface.
Otherwise, you won't get very good performance from your brakes.
Then if you lost a lot of pad, it was probably because you didn't bed in your pads before you drove on the track.
2015 F34 328iX GT Glacier Silver
2011 E90 M3 Monte Carlo Blue
2004 E46 M3 Imola Red