Factually, you can have listeria and not show symptoms initially. However, something like spoiled food, if it really had spoiled, would have upset your stomach in a more immediate way. Ultimately though, what's done is done. You can't go back and change it and there's no pill you can take to stop yourself from getting sick so try not to worry about it.
This. If you haven't gotten sick yet, you're unlikely to get typical "food poisoning" symptoms. You can let your doctor know at your next visit......That said, listeria is pretty rare, so hopefully you'll be just fine. You can try checking the ingredients on the dip- a lot of the jarred/on the shelf type dips don't have real dairy in them and I think the refrigeration directions are just so that they last longer.