Your feelings with your first cum almost exactly match mine. I was ten. I was alone in the house during the summer holidays and bored. I had been playing with my cock for some time, but not seriously, though it had been getting stiff. This afternoon I carried on because it felt so nice. I was astonished when white stuff started to ooze from my cock. It went all over my fingers and on to the floor and smelled really strong. I felt dizzy and had to sit down and like you thought I had done some damage. I vowed not to do it again and hoped my cock would stop going stiff when I saw girls. Like you the next night I wanked again and this led to a lifetime of wanking.