Naw. You thinking too much.
Everything that happened before this movie is a different timeline.
Captain America DID mess up the timeline by staying in the past.
He pulled a "Flashpoint".
He was not supposed to stay in the past.
He was there and there was another Captain America there. So I wanna know how this works out????
You're half right. The only way it doesn't work is if they pull Captain America out of the ice, then there would be two. Otherwise, Cap stays in the ice and the Cap who went back to 1970 lives out his life there.
They create a different timeline once they change something, but they can always jump back to the timeline from which they came.


