I don't think I'd mention the ice cream thing again. I'd just casually say "hey" or something. I feel like you did your part by making the first move and giving him your number and inviting him for ice cream. Now the ball is in his court. IMO, if you bring up the ice cream again, he'll think you're desperate. Let him make the next move. If he doesn't, his loss.
Stay positive and remember to be yourself. He was interested before you even knew that he existed. He likes the person that you are so have faith in that. Don't stress over the ice cream, either way.
