All you've heard so far is right; A butterfly on it just as it happened would be best, but half a day on you may have lost some cells in there that could have knit back up. No matter, it will make a very distinctive ornamental scar, if it scars at all! Young dudes' skin heals miraculously...
A can of bandages kept nearby is an absolute must for craftsmen!! Go to the drugstore and get as many assorted shapes as possible (definitely look for butterflies, they're mandatory for anyone using X-Acto knives!), and I strongly suggest cloth bandages: they stick and flex much better, and this is something you don't scrimp on.
I agree with Sp'-9: you should make up a better story. We'll help. Around my neighborhood, it'd be "jostled getting on the Subway" or "that nasty demonstrator threw a brick" (the N.D.'s politics can vary depending on who you're talking to...)