HOW do I toned down the sharpness in a tomato sauce

1/4 teaspoon of baking soda, thoroughly stirred through it, also works well. I find that baking soda doesn't change the flavor of the sauce, as sugar sometimes does. ;o)

Add sufficient salt - it takes more than you’d think but do it gradually the first time to make sure you don’t go to heavy.

You can add a few pinches of sugar and whisk in a couple tablespoons of butter.