Now, now; there, there. As malmo suggests, with seven weeks of more consistent training you should be fine.
TBH I'd be just as focused on sleep as on mileage, particularly as you're building that mileage up. My (personal and anecdotal) impression is that a lot of HS guys get short and/or inconsistent sleep during the summer.
Go to bed and wake up about the same time every day (weekends included); go to bed "today" (before midnight); go to bed a half-hour before you're used to; get away from all screens (TV, computer, phone) a half-hour before that.
Basically, there's a choice: having "a lot of fun" in the summer, or having a lot of satisfaction from xc in the fall--you'll decide. As a rising junior, you're likely to still be growing, and virtually all growth (and anabolism and tissue repair) takes place when you sleep. Choose wisely, grasshopper.