Masturbation is normal physiological act and it does not cause harm. You should not feel guilty about your normal physiological urges. Attraction towards opposite sex is normal but compulsion to masturbate is unhealthy. Self control is required to overcome this thinking pattern.
Your penile length is an average. Always remember that Female’s sexual satisfaction does not depend on penile length. It depends upon your love & affection for her, quality of intimate moments, warmth in relationship and many other nonsexual factors.