Resonance structures don't technically exist in actual molecules because the electrons are flicking about so quickly.
They are just possible states for the bond configurations in a "freeze-frame" of time.
Think of them as contributing portions to the overall character of the actual molecule, rather than being independent molecules.
The more stable structure(s) will contribute more to the actual character of the molecule than the less stable ones.
Thus, even though it is not favored, the less stable one is represented in the molecule as well, simply because it is a plausible configuration of the bonds.