There are many different ways to measure the left atrium when a complete echocardiogram is performed. This includes diameter (using M-mode) as well as volume - which is calculated in a variety of ways. Not all of them will agree as you are trying to measure using 2-dimensional imaging. However, one of the most commonly accepted volumes is the "indexed volume" which is reported in ml/m2. A mildly abnormal LA volume by the American Society of Echocardiogram is reported as 29-33 ml/m2 (moderately: 34-39, severely abnormal: 40 and above).
I would call the doctor that ordered the echo & confirm that measurement before I got worked up. Bet it's a typo error.