I was just looking at your blog in graph mode, and there are two big standouts to me (although from your last reply it sounds like you haven't added in all your miles or something):
1) Mileage. If you want to run a good high school 5k, you should be running a lot more than 10-15 miles per week. Even just slowly working up to 40 miles per week with a long run of 10-12 miles once a week will likely put you closer to the front of your average local 5k and will probably get you down near 17:00, assuming you are capable of a 5:00 mile. If you can work up to 50 mpw, that's even better.
2) Pacing. Slow down. You don't need to constantly run at lactic threshold or VO2 Max to get where you want to be. Even training for a 5k, most of your mileage should be easy. You should be able to easily carry on a conversation. Speed and/or conditioning workouts should be targeted and should not make up the bulk of one's training at your level. Most of each of those columns on your graph ought to be blue. You are doing a great job doing the RIGHT kind of speed/conditioning (400s, 800s, 1000s, etc are great for a 5k!), so definitely keep that up, but just do a little less of it. If I were in your shoes, I would probably confine myself to two of those types of workouts per week, still do slow mileage on those days as a warmup and cooldown, and let everything else be slow and easy. And when you do get speed work in, don't be afraid to push hard. Push hard enough that it forces you to go easy on the other days. If you are resting correctly between hard days, you will be able to have much higher quality speed days while still getting appropriate mileage. If you really are itching to get your legs going all the time, do 4x100m strides or accelerations after your easy miles. Or maybe a couple of relaxed 200s. But nothing that will make you sore and tired for your hard days. I know I was the same way as you in high school and for a couple of years after. I was always wanting to go out and blow everyone off the track every day and impress the pretty girls (unfortunately I was not very successful in that last part--too skinny), so I had to consciously work to relax and calm down with some help from a very wise coach. It paid off in the end, and it will for you too. 18:00 will seem like cake if you train smart.
Hope that helps. Good luck on the race, and future races.