Travis, which tested approved for canning salsa recipe are you using - I don't know of any that substitute citric acid for measured amounts of commercially bottled vinegar, or commercially bottled lime or lemon juice. If you've measured accurately and are following a tested recipe, there would be no need for additional acidity. If you are omitting vinegar or lime juice, you will have a density issue among other things....

"I am afraid I'm going to get botulism, unless I follow a recipe exactly. I wonder what amount of citric acid to add to the mixture to make it safe?"

I'm sorry but it doesn't work that way. First the recipe you use has to be tested and approved for pH balance. You can't just make up your own amounts. That balance is determined by the ratio of the ingredients and their pH to the amount of vinegar (or bottled lemon juice) called for in the recipe and most recipes require at least 1 cup of vinegar or more. You don't mention any added acid at all. Only then can you determine how much citric acid to add if necessary.

So without knowing the exact recipe/instructions you are using there is no way to know how much citric acid, if any, might be required.

For example: http://nchfp.uga.edu/how/can_salsa/tomato_salsa_paste_tomatoes.html

calls for 7 qts tomatoes and 9.5 cups chopped peppers and onions AND 2 cups of lemon juice. You have 18 and 5.

The standard dose for citric acid for canning plain tomatoes - added to each jar - is 1/2 tsp per quart, 1/4 tsp. per pint. But that is for tomatoes only and can't come close to covering peppers and onions. And we have no conversion tables for CA to vinegar, only a rough estimate from the acidification guidelines that

1 T bottled lemon juice is supposedly equal to 2 T 5% vinegar or to 1/4 tsp citric acid.

Dave