It called for cooked shredded beets, raw chopped cabbage, horseradish, sugar and salt, packed in jars and cover w. vinegar.Nothing else. That seemed inadequate, so I added a cup of vinegar to the mix, put it in jars, and did a boiling water bath for 12 minutes. I was uneasy, so have put the jars in the fridge. They all sealed. Should I throw out the lot?
Always post the original recipe for this kind of question if you don't mind. But you increased the acidity of the mix, pasteurized them, and refrigerated them. Nothing you did here was unsafe.
The flavor and texture are going to be different. Vinegar will actually halt the spicy-fying process that horseradish undergoes, so the mix might be milder.
But as long as you keep the unopened jars refrigerated, see no sign of spoilage, and like the stuff you've got, it should be alright.
The only thought I have against your process is if the vinegar was supposed to start a fermentation process, which might have produced more vinegar than you added. Your recipe should tell you if that's intended. So maybe it won't be as sour.
If you really feel uncomfortable at all though, there's no shame in tossing it and starting over once you've done more research into the preservation process you're using. Better safe than sorry.