Here is the Issue: I installed an outlet on the opposite side of the wall of an existing outlet. And wired it with 14. This run is around a foot. The outlet I ran it from has an 15 AMP outlet but the wire feeding it is 12 and is on a 20 AMP breaker. I didn't notice this until I was done wiring it. Is this unsafe should I bother rewiring it?

Rewire. Not safe, not to code. All wiring behind a 20 amp breaker must be 12 gauge or larger.

To confirm, HK is correct.

Change the wire to #12, or change the breaker to a 15 amp.