I am taking a meal to a family tonight, my sauce is cooking, it will cook for several more hours. Right now, it is much too strong, ( I know, I did not think it possible). How do I cut that flavor?
The punchy, raw flavor of garlic is very volatile, and it'll change as the sauce cooks. Garlic (like all alliums) gets a lot more mellow as it cooks, and the extremely intense flavor you're tasting now will fade into the background.
So you simply may not need to do much now - taste the sauce again in a couple hours and re-evaluate. There's not a lot that you can do to target the garlic flavor specifically, other than adding more of the other ingredients to restore the overall balance of the sauce. If your overall cooking time is, say, 6 hours, and you check in another 2, that still leaves you a decent amount of time to add more of everything else for the last few hours of cooking.
But don't panic immediately; give it a little time and see how well it mellows out. It's likely fine and you have ample time to make more corrections.
OK, my first thought is "garlic good, keeps vampires away". OK, so I like stronger garlic than many find socially acceptable. But in the future, if you are worried about to strong, harsh, roast it first to speed up the mellowing, or lightly saute in oil before you add to the sauce. Too much will turn it bitter.
In some dishes you can add dairy, but if you are making a tomato sauce, that is likely not an option.
Acid will help mask, but again, if you are doing a tomato sauce, you likely have plenty of acid already and are doing a long cook to mellow that out as well. When it is an option, add lemon, vinegar, wine, etc and some of the garlic will likely be masked.
Aromatics will mask some of the garlic to many tastes, basil or cilantro are often targeted, but parsley, a relatively neutral herb can also work without radically changing your sauce flavor. Like garlic though, too much can turn your sauce bitter.
Sweetening with sugar can cover, but is not always a choice for some sauces, but adding more sweet onion is often used as it can both sweeten without losing the savory nature of the dish, and compete with the garlic.
I would not go with any of those though until after giving time to see it the garlic will simply mellow out for you.