How should I train for cross country season?

I am a 16 yr old female running JV cross country. I am entering junior year of hs, and running about 20 miles a week so far this summer. I have run about a 30 min 5k. I was supposed to take off a couple minutes last year, but suffered a quad strain. Now healed, I have been running for about 3 weeks, just trying to build up a base again. The season starts in the fall, racing 5k. How should I train to gain speed without risking injury? More mileage? Two a days? Cross training? My runs average 3 miles, once a day, 5 or 6 days a week. I have a gym membership and pool. Also, what is a realistic goal time by the end of season(November)? Hope you can help a fellow runner! All answers appreciated:)