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?

Thank you very much for your
question and congratulations on your recent Botox treatment. It will take from
one to two weeks for the results from your Botox to become apparent. At three
days post-treatment, it is too early to note any results. Over the next several
days, you should start to see some changes in your jawline. If you have any
further questions, I recommend contacting your Botox provider.

You have received an adequate dose of Botox.
The effect of Botox (muscle paralysis) starts at four days.
Botox's full effect (paralysis) occurs at two weeks.
It takes six weeks to visually observe shrinkage (atrophy) of the masseter muscles after Botox injection.
Be patient. 

It can take as long as a week or two to see the effects from a Botox treatment, so it is not unusual that you see no effect on your masseter muscles 3 days after your injection.  You will first notice that the muscle does not clench as much and then over more time, you will see a slimming effect.