It might not be the best solution but I can think of two ways that you can do this.
You might want to make you character stationary and move the world towards your character and set your character’s location mixed with a timeline node so it smoothly transitions lanes.
Other way is that you can set a constant move forward and get movement input from your character with a boolean which stops registering left or right movement when your character reaches certain Y location.
Or adding timeline node to your current setup might help smoothing the transition.
Having it directly switch lanes might give you a hard time setting up animations rather than giving it the freedom to move in a range, but it’s doable.