Well my friend, you are at the defining moment of all track athletes careers. Injury before high school end of year events. We all have been there. Theres two roads to take. If your racing next year, my advice would be to do your RICE, and be conservative. Back injuries can get sticky if not taken care of properly. BUT if your not racing again and this race is very important Ice it big time and stretch it out. Then when you want to compete alternate with heat. The day of the race heat it up, DO NOT USE ICE after you heat it this time, the heat will loosen the muscles and allow you to get the motion your looking for. Its probably gonna hurt big time still. You will probably will have to have taken a few extra IBprof then usual. If you take 2 like normal people throw in a third for good measure. (If your like some people I know and live on 5-10 IBprof a day you may want to go get your kidneys and liver checked.) I had the same thing, I yanked a muscle in my neck the day before states. I ended up having my neck taped immobile and throwing back a bunch of pain meds. Ran a great time.
Sometimes you just have to man up and run.