I'm not sure to the extent to which you hurt yourself, but could it be pulled off as animal skratches (i.e. cat? - if you have one) ... or if you can, can you cover it up with bandages and say that you clumsely fell and cut yourself on a corner? .... I'm sorry if these don't work ... unfortunately i'm not the best at lying either

Hope that things go okay tomorrow ...
Jacq