Detecting left and right being pressed at the same time.

I'm working on a 2D platformer and one of the things I want to implement is zeroing out the player's X velocity if both left and right are being pressed at the same time. Almost everything I've tried in code hasn't worked at all unless both keys are pressed down starting at the same time. What I want to do is, if the player is holding right and then starts pressing left at the same time, they come to a stop.

     if (Input.GetKey("left")) {
         transform.localScale = Vector2(-1,1);
         physics.velocity.x += Input.GetAxis("Horizontal") * physics.maxVelocity.x * 2;
     } else if (Input.GetKey("right")) {
         transform.localScale = Vector2(1,1);
         physics.velocity.x += Input.GetAxis("Horizontal") * physics.maxVelocity.x * 2;
     } else {
         physics.velocity.x = 0;
     }

Also, since it'll probably come up, I'm using GetKey because GetAxis takes some time to come to a stop when I want the character to be able to stop on a dime.