In my adolescent age I faced similar situations. And in India, we had rotten system that calls every young person to ‘save semen’ and make a reservoir of it within that helps in getting us enlightened! So I was very worried too, but by the grace of god I came to know from Q&A series in a foreign magazine ‘The Sun’ that it is not harmful. As per science our body can produce as much as it needs, especially in young age.
It is good to get ourself satisfied till we are not having any partner.