How to friend zone?

Sierra

How to I make sure that someone knows I just want to be friends? We both said that we didn't want a relationship, but he's admitted that he had a crush on me in the past, he keeps calling me cute, and he recently asked if he could buy me an ice cream one day. I want to make it SUPER clear that I only want to be friends. I don't want to have go through friend zoning him again after this.