Correct, you do indeed have a Hero helmet so you will need to add top rivets to your Stunt belt, you can't apply with mixed versions.
Here are the CRL's for each if you would like to check anything
Hero https://databank.501st.com/databank/Costuming:TK_anh_hero
The holster is affixed with four fasteners, two on the top, two on the bottom (two per strap).
Fasteners may be rivets, snaps, or Chicago screws.
Stunt https://databank.501st.com/databank/Costuming:TK_anh_stunt
The holster is affixed only two fasteners at the bottom, one on each side.
Fasteners may be rivets, snaps, or Chicago screws.