The scar has widened because of motion at the knee creating distracting forces on the scar edges. That will not change if you cut out the scar to make a new one as long as the knee moves. In fact it could make things worse. In my experience this is as good as it gets-sorry to say so.
My response to your question/post does not represent formal medical advice or constitute a doctor patient relationship. You need to consult with i.e. personally see a board certified plastic surgeon in order...