Hi Margot. I am in a very similar situation to you. I went to my primary care doctor in early December because of an ear problem. Since I hadn't been for a physical that year, he had me do the normal lab work. The urine test came back positive for the presence of blood, so he had me get a CT scan at the hospital with which he's associated. I had that scan and it came back with a reading of a small lesion (1.5cm) on my right kidney. Ultrasound was suggested to verify the composition of the mass. I had it done at the same hospital. After performing the first ultrasound, the tech came back and said the radiologist wanted another reading. After that reading, the radiologist came and asked if he could take a reading. None of the three readings found anything, so they suggested a multi-phasic CT scan, which I had at the same hospital on New Year's Eve. That came back as suspicious for renal cell carcinoma and suggested a urological consult. I told my primary that I didn't want to be referred to anyone associated with that hospital, as I think they intentionally messed up the second CT scan, so fortunately, my insurance allowed me to be referred to a urologist at Stanford. I saw him in January. His suggestion was to wait and see, as 1.5cm is incredibly small. He also confirmed my suspicions that the second CT scan was not done correctly. I just had a scan done at Stanford, so he could compare the December results with a new July result. Apparently the lesion grew from 1.5cm to 1.6cm. So, it's a very, very slow growing lesion. I go back to see the urologist this coming Thursday to find out what the course of treatment, if any, is going to be.
If you have a 2cm lesion, it does seem like a pretty common practice to wait and see what develops. The Stanford urologist told me in January that there's little risk of these things growing rapidly and spreading. He was willing to remove it in January if I felt uncomfortable with the prospect of possibly having something malignant inside me, but he felt that the watch an wait approach was better as he didn't want to cause me to have reduced kidney function unless there was clearer evidence that the lesion was, in fact, malignant.
My suggestion to you is if you feel uncomfortable to go and have the ultrasound repeated earlier. Unlike my situation, where they needed to do a CT scan with all the attendant radiation that goes with it, an ultrasound has no such issues with radiation, so you could get one every day and not be adversely affected. It sounds like you'd like to have the peace of mind of knowing what's going on inside.