What's the best way to tell your mom that you are in a big, BIG trouble without her, if possible, not getting angry?

my parents went away for business so I was left with the responsibility of taking care of my brother and making life as normal possible for him even though mom and dad are not around. the problem is, i failed a subject and now because of that failure, i became an irregular student meaning i was only allowed to take up the minor subjects MEANING instead of graduating in 2011, now they have to waste money on me for another added year. education is like really a big deal in our family and they have expectations for me. mom’s coming back from their trip. any tips on how do i tell without her possibly taking me out of the family tree? lol