You need to go to the dentist and get an X-ray done so the condition of the root canal treatment can be analysed better.If infection is shown in xray then u need to start a course of antibiotics and get the root canal done again properly….and after all the swelling and tenderness gone then go for the capping part.
Next Steps
You should start with the antibiotic course first.
Health Tips
When you go to the dentist this time make sure you take a picture of the xray before starting the treatment and a picture after the re-rct treatment done fully so that you get a better idea how the treatment went and for future reference if the same tooth troubled you again