Based on the way your track times looked, you probably didn't run during the winter before spring track, right? You have a huge slowdown between one mile and two (and a bit more of a slowdown than expected from 800 to 1600). While it is expected that your pace will slow some as the distances increase, the amount of that slowdown is often indicative of your mileage and how much training you've done. The amount of slowdown that your track times tells us that your preseason mileage was low or nonexistent, but you worked hard once practice started.
Now jump to your 5k pr, compared to your mile and 2 mile times. The slowdown from 2 to 3.1 miles isn't nearly as prominent - you probably ran some this summer before XC started.
The key to high school running success is preseason mileage. After XC ends, take about 2 weeks off completely from running. Then start working on some mileage for spring track. There are a ton of online resources for off-season training programs, check out several and find a schedule that suits you. Based on your spring times, I'd suggest something that is not too aggressive early in the winter, something that builds slowly. You appear to have a good aptitude for running, but training at a very high level can't be sustained from November all the way to spring track.
There is no way to predict how much a person can improve. You've got such a long time until college, anything could happen between now and then. Generally speaking, in sports (and any other activity in life), the only way to tell if you can do something is to try and do it.