Has any salivary gland pathology been ruled out? However since you have undergone RCT, it is prudent to wait for atleast a week for everything to settle down. If the swelling persists after a week, then you must consult an oral & maxillofacial surgeon or a good reviews general dentist. Swelling / lump is the neck is a cause of concern, so go for a review.
Next Steps
As of now follow the advise of your dentist who has done the RCT. In case the symptoms persist and the pain is increasing, consult ur dentist without any delay
Health Tips
Trust and follow the advise of ur dentist. However if you are in doubt and want a second opinion. You may connect with me or any good reviewed dentist.