My 3 yr old will not ever say he's sorry whether it's an accident or deliberate behavior.?

Today we were at the beach and he and his friend took a little girls doll and threw it into the water. The other child went and apologized. My boy did not. I told him we could not stay and play if he did not say he's sorry. He'd rather go home. He actually is very empathetic and gets very embarred. How do I empower him (we do make it a point as parents to apologize when needed, so the example is there) to say he is sorry? As we were leaving today, I was wondering if that was the right way to handle it - by running away...but we sure weren't going to stay and play like everything is all fine! I'm at a loss. HELP! I was so embarred and felt horrible for the little girl...and her mom!!