I will let one of the @HealthExperts interpret your results, as I am not a medical professional. I might say that the majority of liver nodules that are found by US are benign and most people who have them would never know unless they were scanned (this is discussed in a similar thread here: Discovery of a liver nodule).
Also, I would not be too concerned with the difference in size between the two measurements. The difference of 1mm could be due to differences in the radiographer measuring the nodule, particularly since they mention that it is very subtle.