In this paper we propose a nonlinear control law to achieve trajectory tracking in the 3D space for a commercial Bebop 2 quadrotor. The proposed control law is based on a nonlinear time varying version of the Backstepping technique, which includes an integral gain for disturbance rejection and that takes into account the dynamics of the internal controller for the orientation of the quadrotor. The stability of the control law is ensured by the design of recursive Lyapunov functions and its performance is tested by real-time experiments.