How is quadrature mixing done?
If your signal's in-phase and quadrature components are $x_I(t)$ and $x_Q(t)$, respectively, then your quadrature mixed signal is

$$s(t)=x_I(t)\cos(\omega_ct)-x_Q(t)\sin(\omega_ct)\tag{1}$$

where $\omega_c$ is the carrier frequency in radians per second. You can also use a '$+$' sign in $(1)$, that's just a matter of convention.