3 days after Botox injection to the masseter to slim the jaw, I don't see any effect, should I go back to the doctor?

Botox results can take 1-2 weeks and will last 3-4 months in new areas of treatment. It may take a series of treatments and a combination approach with radiofrequency to get improvement. See an expert. Best, Dr. Emer

Botox takes two full weeks to take effect.  If after that you don't see any effect return to your provider.