You could always rope in your head of year or (as swsummer said) guidance teacher. If you just send an email instead and say "I wasn't assigned a class, could you please let me know where I should go", then you wouldn't even have to face the teacher, and it's very matter of fact. Instead of over apologising you can take a matter-at-hand kind of approach where you appear stronger and are just trying to sort out a problem. As long as you don't seem cocky or annoying. This teacher doesn't sound very nice if that's the way they reacted, but many teachers especially sports teachers are like that, you just have to find a way to stand your ground sometimes.