I had active monitoring done for 2-1/2 years before the doctors decided the lesion on my kidney had grown enough to warrant taking some action. On June 22nd, I had a robotic assisted laparoscopic partial nephrectomy. The surgeon removed an area that was 3cm x 2cm x 2cm, so quite small. They tested it there to ensure that they had taken out the entire lesion, and they had. I believe the term of art is no negative edges. I had the operation at 3PM on the 22nd and was discharged at 1:30PM on the 23rd. Very fast. The pathology report came a week later and it confirmed that it was something called chromophobe renal cell carcinoma. It's a form of the disease that only occurs about 5% of the time, so pretty unusual. It's a very, very non-aggressive form. It rarely spreads beyond the kidney (and mine hadn't) and it rarely comes back. But, just like you, I'll be having scans every six months for a while. And that's fine with me. I'd rather find out about something early enough to do something about it.
Just so you now, when I started this whole thing, it was December, 2013. routine physical uncovered microscopic amounts of blood in my urine. So my primary doctor had me get a scan, thinking it was a kidney stone. It turned out to be a lesion. I was referred to a urologist, who said that the standard of care for something that small (it was 1.5cm at the time) was active monitoring. So, I had a very similar circumstance to yours.
If you haven't already, it would probably be a good idea to get a referral to a urologist who specializes in cancers of this type. That's not to say that you definitely have it. But a regular urologist will see only a few cancer cases, seeing instead probably a lot of prostate issues in men and general types of urological problems in everyone else, a urological oncologist will know a lot more about kidney issues like ours.
The very good news about your situation is that what you're dealing with is so small that even if it is malignant, the technology that's available now is simply amazing and results in a total cure in about 98% or 99% of all cases that are caught at the stage we're both in.