If I flunk tomorrow,....

Another way to say it.

From the context, it appears it might be a kid/teenager talking about the possibility of failing miserably on a test/exam. The idea of failing in this way is often communicated, at least among American youth, with the adverb "totally," as in: "(Dude), if I totally flunk that exam,..."

This type of usage is common, especially in California (surfer) youth culture, which has had an effect on standard youth speech throughout the country (dating back to the days of Sean Penn in "'High Times' at Ridgemont High" popularizing the use of "dude"). :-)

Other options might include "completely" or "miserably" (though the last one might be too standard in this context). :-)