First of everyone is right. You need to take at least a day or two in order to evaluate just how badly you hurt yourself. Having played a lot of soccer in my life I have pulled, strained more than my fair share of muscles. Many times a day or two is really all you need to feel good again.
Take some time to ice, motrin, stretch lightly and all of that. Then see how you feel.
The last thing you want to do is show up to your race half hurt and end up not finishing or in bigtime pain while you are in route. Undertrained and healthy beats fully fit and unhealthy everytime.
Well, unless it's me vs. Ryan Hall. That guy could beat me with a broken hip I think.