Stop Horizontal Movement Inputs while Dashing Down (2D)

I recently implemented a simple code for dashing downwards while in the air. The issue I'm having is that I want to stop the player from being able to move left/right while the dash is taking place. I've tried setting the horizontal value to 0 but this doesn't seem to overwrite the current horizontal movement code. Here are some lines from the code I think have to do with the issue:

Code (CSharp):

1.         // If player is not grounded, then dash downwards
2.         if (!IsGrounded() && Input.GetKeyDown(KeyCode.Q))
3.         {
4.             rb.velocity = new Vector2(0f, transform.localScale.y * -downPower);
5.         }

Here is my horizontal movement code:

Code (CSharp):

1. horizontal = Input.GetAxisRaw("Horizontal");

Any advice would help. Thank you!