Had 5 day holter, ekg, stress test, cardio says heart is good. still get chest tightness and smart watch reads afib with ecg. should i get a 2nd opinion?

A second opinion is always a good choice if any uncertainty exists with a given diagnosis. With a Holter/EKG/stress test, your "smart watch" may be incorrect, but for peace of mind, a second cardiology exam is a good idea.

Smart watch is not always smart enough. Recording has to be clear without artefacts and should be read by cardiologist. Cardiologist's opinion that the heart "is good" does not rule out a paroxysmal arrhythmia. Unlikely, based on the multiple tests you have undergone. Please have your doctor see the recorded signal.