Animation won't complete unless button is held

Hey there, I'm getting really irritated by this problem :s. I have an animation that I need to play to switch weapons, but the animation won't play unless I am holding down the button? Even when using GetButtonDown it only plays it for half a second then stops because the button has already been pressed.

The following code is what I have so far,

 void FixedUpdate()
 {
    if (Input.GetButtonDown("Swap"))
    {
        WeaponSwitch();
    }
 }
 
 protected virtual void WeaponSwitch()
 {
         
     if (weaponSwitching)
         return;
 
         weaponSwitching = true;
         weaponSwitchTime =             weaponAnimationHolder.animation["SniperToSMG"].length;
 
         weaponAnimationHolder.animation["SniperToSMG"].speed = weaponSwitchTime;
         weaponAnimationHolder.animation.Play("SniperToSMG", PlayMode.StopAll);
         
         StartCoroutine(waitFor(weaponSwitchTime));
 
         weaponSwitching = false;
 }
 
 IEnumerator waitFor(float waitTime)
 {
    yield return new WaitForSeconds(waitTime);
 }

Could somebody please tell me how to fix this? All I want is my animation "SniperToSMG" to play once without the need to hold down a key.