Okay, I don't know who's gonna see this, but this is advice that I always gave to my friends, and my little brother's friends.
I haven't been a teenager for a while, and found this on /r/all, but here you go:
When I ask someone out, I'm clear; "I want to ask you out to the movies on a date./Just the two of us, as a date/etc..."
One time in highschool, a girl didn't actually know that I was interested in her, which I learned a few years later when she told me that she used to have a crush on me, and I decided not to have thtat problem again.
Most people are really good at returning to "normal" after a short time after, especially if you're mature about the situation.
My go-to has always been: "Look, I really like you, but I also really value you as a friend. I would love to be able to take you out on a date if you're interested, but if you aren't, just give me a few days to get over it, and then we can be firends again."
(I'm not quite sober so just imagine that I phrased those better, and don't send the whole "I like you but here's the alternative" paragraph all at once, but you get the idea.)
Good luck.