My Friend Is Denying to Get My Money After I Used Some of His

So here is what happened…

We were at a gas station getting snacks when I forgot my wallet. My friend said that he can pay for what I buy that’s not too much. I give a polite thank you then we got the snacks. Now I want to pay back by getting him 5$ (CAD). He denied it 2 times. I don’t know what to do, it’s just a lot of money to me.