embarassed of my son

Yesterday I took my kid (4 yo) to buy groceries. Usually, I don't bring him, but because yesterday there was no one to look after him at home, so I brought them... at the store, he saw chocolates and wanted them. I said softly, not now, sweetie, the dentist said your teeth will get ruined. You're not allowed to eat that too often... I felt so embarrassed, he immediately started crying and screaming. he even threw a tantrum. I was really embarrassed. I wanted to run away but that's my kid. I stayed quiet and cried until someone helped me saying it's okay... Finally, I took my kid out of the store and didn't go shopping. Has anyone had a similar experience?