Well to me that sounds kind of stupid. I don't know if your friend got into any sort of trouble after you "ratted him out" but I can say that telling your coach that you friend simply did not attend something that I'd rather be doing than working isn't that bad. I mean...It's not like it's a SECRET that he didn't go (I'll assume that your coach has a way of keeping attendance). If your coach didn't take attendance for these mandatory activities, then they shouldn't be mandatory because there's no point in anyone showing up.
You don't need forgivness from a friend who's basically a hypocrit (he ratted YOU out to the whole team for "ratting"). I mean yeah, you don't snitch but hell, what you did wasnt snitching unless you had the intent of getting him into trouble. Sure, say sorry because you didn't mean to "tell on him" but that's that. If he's still mad, tell him to stop being such a little girl and quit his mellow drama. I don't tolerate friends who pull this kind of crap and neither should you.
No respectable friend spreads rumours and spills secrets. That's highschool clique crap. If he wants a fight, give him one.