Hi sir. Do not worry. How is the dog now?
Scratch is a Category 1 wound if it's a domestic dog. As long as you washed it with soap and water, there is no need to worry now.
Vaccine will not help now, after 3years. If the dog is fine or was fine for a few months after scratching you, then it was probably not infected.
Next Steps
Do not worry.
Health Tips
After a dog bite, wash with soap/detergent and running water
Do not dress the wound or stitch it
Get a Rabies Vaccine immediately