What should I do to get the record?

I'm a female junior high runner. Our school's mile record is 5:34 and I want to break it. A few days ago I raced a 5:47 after not having run for a month because of an injury. I had started running 2 days before the race. Just today I did a workout consisting of 9 minutes of fast paced warmup running, and a 1:50 min. third of a mile, followed by a 300m walk, and then a 1:55 and then a verrrrry slow 300m walk, and then a 1:49. (I was trying for all 1:50s, but oh well). It left me exhausted, and I need to know some other workouts other than that one that will help me achieve my goal of breaking the record. What are your suggestions? Also, do u think my goal is manageable?