I had a tiny spot of micro leakage on a composite filling on a molar that I wanted repaired without removing the whole filling.

I clearly emphasized to the dentist do only that little spot. He did two molars, the one turned out good but the other tooth looks like another layer of filling on top of the old and covers enamel that wasn't covered before. That tooth did have some minor decay under the spot he was supposed to do. I don't know if he decided to do around the rest of the edges that looked sealed to me? This is stressing me out!! What is the worst that could happen to this tooth? Can it also turn out fine?