Facial asymmetry due to differential muscle blocking response to Botox is self-limiting and often takes several weeks to months to gradually improve.
Alternatively, careful placement of touch up Botox to the side that has a poorer response to the earlier Botox injections may help address the facial asymmetry faster within 1-2 weeks.
A proper assessment by your attending doctor who treated you in the first place is most important to address your concerns as he/she knows how much Botox was used and where he/she injected into.