I don't have enough sour cream, could i use a cup of heavy whip to make up for it?

I used 1 cup sour cream and 6 oz of greek yogurt and the rest heavy cream. It was delicious.

You could, but it would definitely change the flavor profile. I'm assuming your sour cream is the full fat sort, so regular cream would be similar in fat and water content. Sour cream is simply a cultured product made by adding bacteria to cream to thicken it. But as you are talking about substituting half of the amount of sour cream called for, I think you would be better off just purchasing additional sour cream to use. Otherwise, it might end up tasting bland and overly rich, coating the mouth with fat and covering up the glory of the peaches.