The size of Left atrium (LA) is dependent upon your body size, any disease of mitral valve, diastolic dysfunction
(impaired relaxation of heart), presence of abnormal rhythms like Atrial fibrillation
, presence of anemia
or other disorders causing high volume circulation and on your intensity of workouts. since you have not mentioned the size of your LA (especially the volume), it is not feasible to calculate that if it truly out of limits for your body size. neither other parameters on your ECHO report are mentioned (i assume they are all normal). if you do not have any other problem in ECHO and you do not have clinical problem, then do not worry, relax and send us its exact size so that we can calculate it for you to give you exact picture.