How can I carry on competing despite injury?

I'm doing a two day heptathlon for possible county selection. The first event was hurdles and I pulled a glute (butt) muscle landing over a practice hurdle funny. It seemed fine but I then went on to high jump/sprint and now I'm home it kills like hell and its really impeding my movement.. Tomorrow I have long jump, javelin and 800, and I know you shouldn't compete injured, but I'm second and I'd like to get through to county... Is there anything I can do to keep the pain/injury at bay for just one day - and then I promise I will rest!!