If you showed your doctor and she said it looks fine, you should relax. Just keep an eye on it like she said.
Asymmetry, irregular border, variations of colors (as in purples, whites, blacks, blues, greens), and diameter are the factors that doctors use to identify problematic moles.
Your mole looks benign to me, but I am no expert.
I only studied this in classes.
If you are concerned about the mole becoming cancerous, my advice would be to go ahead and have it removed while it is early.
This way, the chances of developing melanoma are dramatically reduced. Make sure to keep a high-factor sunscreen on that area until then.