I haven't heard it need to take 3 dose.
Only 2 dose for child for the first time.
That is if you your child 打 this year 2 dose, then next year and onwards if you want, then take 1 dose is enough.
I think your doctor is tricky and not trustable. He said "出年一次", I think it's just what we will take the dose 1 year 1 time. If I were you, I will not go to visit this doctor again.