There aren’t many hard and fast rules about what goes where.
Yes, we put participation in math education, competition, etc, in Activities (AMC/ARML/MPfG/PuMAC/HMMT/JHMT/CMIMC/etc).
I’d put Winner/Honorable Mention at *AMO, prize winner at ARML (22 this year), and similar in the Awards section. But not HR/DHR/Achievement etc that are broadly “awarded”. Certainly not participation.