Not the ending I was expecting (spoilers)

my prediction for the plot was that he was going to go around the school filming himself telling everyone it was his last day and not being taken seriously, then after his friends wanted to make it a pact have them wait in some place to get them out of the way, then at the end turn to the audience and open his backpack to reveal that he brought more ammunition then one would bring if he was just planning to kill himself, then have the big twist being him going on a shooting rampage with his friends not realizing that that was his plan all along.