My Secret Note Joke Went Too Far At School

Okay, so I've been feeling pretty petty lately. The other day in school, there was this kid named Alex who always seemed to get the best grades and everyone admired him for his intelligence. I'm not going to lie, sometimes it can be a bit frustrating seeing someone else succeed when you feel like you're working just as hard. Anyway, one day, while I was sitting at my desk in class, I decided to write this little note that read, 'Alex is overrated,' and slipped it into his locker during lunch break. I thought nothing of it until the next morning when Alex showed up with a letter addressed to me, basically asking if there were any issues between us. Of course, no one else knew about my little joke, but I suddenly felt terrible for even writing that note in the first place. Here's where things get really awkward: later on during our class meeting, Alex called out this thing I said about him being overrated, and he actually started to talk about some of his struggles with grades too. Turns out, there was another kid who had been sending him similar notes anonymously and making him feel bad. I've felt so guilty ever since because now I know that what I did might have affected Alex way more than I thought it would. Not only that, but I made things worse by bringing up the note when everyone else was just trying to help Alex out of a tough spot with his grades. I keep wondering if this is normal teenage behavior, or am I really an asshole for doing something so petty and then making it worse? Should I talk to Alex about my mistake now or leave it alone since I'm not the only one who's done similar things? What do you think? Is there a right way to handle something like this?