I think you need to keep in mind that ideas, such as "strings", are conceptual tools to allow us to have some sort of visual representation in our brains of something that we can never see or understand except by a process of analogy. There are, of course, no real "strings". If you think about it, you'll begin to see. What would they be made of? Cotton? LOL. You see what I mean.
But your idea of anti-vibrations is just as good as any other analogy, and right up there among the best ways to look at it. Remember that all matter comes from nothing, literally. Totally empty space still has an energy potential and virtual particles are created and destroyed within it. Hard to believe, until someone actually catches some before they mutually annihilate. So the fact that they come from nothing means that they need to add up to nothing when the whole process is over. The only way that can happen is if they are exact opposites, like a 1 and -1. That way, any particles that come into existence can go back to non-existence without leaving anything behind.
Make any sense?
Strangely enough, this all comes from the Uncertainty Principle. We cannot determine exactly where a particle is if we know how fast it moves, and vice versa. Thus the limerick:
Higgledy piggledy,
Herr Werner Heisenberg said
"But Your Honor, it just isn't fair,
That I was speeding is unascertainable,
And if I was, then I can't have been there!"
Not only do we not know where a particle is, we don't know where it is not, and we don't know when it does not "not" exist, meaning "does" exist.
The fact that the universe is mostly matter means that they cannot be exact opposites. There needs to be some asymmetry somewhere that tends to favor the matter.