Does the doctor's statement that not exaggerating the problem of disobeying parents and forgetting it does not contradict religion, and does justifying oneself to relieve sadness over a sin that has been previously repented of make the repentance unacceptable?

The doctor's statement does not contradict religion, and the questioner's action does not contradict repentance. The boy, being thirteen, has likely not reached puberty. Even if this occurred after puberty, repentance, remorse, and the mother's satisfaction are sufficient, based on the Prophet's (peace be upon him) sayings: "Regret is repentance," and "The one who repents from sin is like one who has no sin."