Botox masseter muscle bulge problem.

You may already be experiencing changes in your masseter from the Botox injection. It may take 2 weeks to see the full effects and for the masseter to smooth. If the bulging persists after 2 weeks schedule a follow up appointment with your injector to assess treatment going forward. You may require additional Botox to this area if the muscle is still contracting. If you are concerned or have further questions contact your injector and express your concerns. All the Best.    

The complication from any injection can be bruising which is indicative of bleeding under the skin. Botox injections are not immune to this side effect and when the injection is deep in the muscle, like those for masseter hypertrophy they can result in bleeding in the muscle or intra-muscular hematoma. This will resolve and can be lessened with topical ice packs held on the areas of injection for 10 minutes every 4 hours for 48 hours. Proper injection technique with small needles and cooling immediately before and after the injection do help to limit localized bruising.

It sounds like you have a hematoma, which is a collection of blood, in the muscle or soft tissue adjacent to the muscle.  This can happen if the needle caused bleeding in the deep tissue.  Hematomas usually don't need any treatment, but occasionally need to be evacuated if large.  The lump will typically resolve over the course of a few weeks with conservative care.