Normally we don't give new characters classes, however since you're here so early in the day here's what I'm going to recommend.
Your character is assigned two "volunteer" classes for the day because the schedules were made before he got there. This basically means you get to choose any 2 classes you want to participate for today for yourself! Simply pick a first class and have your character walk in. If the teacher character or anyone else questions it, your character can simply reference the schedule mishap as a legit IC reason to be there.