Needs work.
You fail to properly acknowledge that Columbine was a failed BOMBING. In fact, bombs placed both to devert police attention and within the school itself. Computer modeling shows that over a hundred people might have died had the propane bombs in the cafeteria exploded. In addition, bombs were placed in their cars were intended to take out respondants to the scene. They only brought the guns to kill the survivors. Failing to acknowledge this is really failure to understand the scope Dylan and Eric had, they wanted to massacre the maximum amount. Eric even went so far as to note the best time to do so.
Apart from that your flash takes elements from really life and places actual events and fuses the two very poorly. The plot as a whole is such an idealization of real life situation that it is pretty offensive to the basic intelligence of the viewer. The map scene with the jocks flowing in ... they didn't want just jocks dead. The bathroom scene where the guy is getting beat up is an idealization too. Eric and Dylan were partners in crime stealing equipment, blowing up pipebombs, etc. before becoming murders, that is how they bonded.