Had ecg and was told atrial enlargement so was referred to a cardiologist,i was told all is normal but letter states resting ecg "possible left atrial?

Don't be concerned: An ECG shows the electrical rhythm of the heart for a few seconds time. By looking at an ECG sometimes one might deduce information about the heart such as size of different chambers. This is only a deduction/hypothesis that needs to be verified typically with imaging. I am assuming the cardiologist performed an echo (US of the heart) that showed all is normal which is why he said so.