It probably is some kind of muscle imbalance. The good news is, when I'm working my hips in a wide range of motions, I make progress very quickly.
As for the post-race week, it's hard to say. I'm a big fan of playing it by feel. My gut would say to actually run 60 or more miles, but make almost ALL of it easy. Since you haven't been doing a ton of short, intense stuff, it might take you a few days to recover from that race (or not and I'm totally forgetting how fast 17 year olds recover).
But either way, when one is in a mileage build and also doing some racing, the tendency is to reach for that little something extra and keep the intensity there. I tend to think of that as getting greedy. It's the kind of thing that leads to more injuries, early peaking, and other problems. But lots of easy mileage tends to make the body feel good and keep the fitness growing (albeit more slowly). Cuz remember, you're training big miles to do well this spring, sure, but you're also training to crush XC and track next year, too. So whatever you end up doing after the race, just make sure you're playing the long game.