Replying to I need an excuse.

So I basically have this job I applied for, I just have to go in today after school to work out the final details. Before I can work, however, I have to attend a Saturday orientation. There is one this Saturday and one in three Saturdays.

The issue is that, for the next three Saturdays, I have to do community service all day. There is no rescheduling of the community service for any reason. I really don't want to tell my new boss that I have community service for obvious reasons, so I need a really good excuse as to why I can't go to the orientations for the next three weeks.

Any ideas are appreciated.