If the key is freshly copied from a place of business … there is a chance that they cut it incorrectly and it has a hook or no ramp which will trap a pin tumbler and makes it damn near impossible to remove.
Another possibility is you are trying to remove it in the wrong position. Make sure the key is straight up and down. (Unless the knob was installed incorrectly).
Was it a locksmith? Or just hardware store Walmart?