How to get better running?

You seem to have a lot of speed, but cross country is about endurance too. My advice is too go on long distance runs 7-10 miles often and mix them with the workouts you've been doing. You're only a freshman and haven't been running very long. You'll be surprised how much you will improve in only one season. You also seem to have a lot of natural talent, I didn't break 19 minutes until my sopre year, but with hard work and practice you should be running around that by states, and don't worry that your times are slow now you took a break and that's why you train in the summer to get back in shape.