Wait, you did not go to your boss in person? Why would you just send and email and just assume you got the days off? True, they should be more willing to work around your classes but you gave them less than a weeks notice that you needed the time off. Everywhere I have worked you requested a day off about 2 weeks in advance, it was no surprise that finals were coming up so you could have requested the time off in....say January if you wanted. In any case enjoy your new found free time...
