Two is not enough.
The appraisal form has four columns, Subject and three comparables. That is four properties to compare not two.
CMA - same thing, at least three comparables.
If you can't find two more then you have to go upsize, downsize, out of area, or out of time and make adjustments. But you have to find two more. Then you can go back to best comparable and state why its the best comparable and why you are using the data from it to determine the value, and not relying so much on the other two.