Im trying to make an animation script in GameMaker

In the script its supposed to run the animation line 6-8 currently and then its supposed to see if down is not pressed and the direction is down then set the sprite to look down Line 23-25 but it keeps playing the animation`x = PlayerObject.x;y = PlayerObject.y;

Direction = "";if (keyboard_check(vk_down)) {    Direction = "Down";    sprite_index = CaseyDownWalk;} else if (keyboard_check(vk_right)) {    Direction = "Right";    sprite_index = CaseyRight;}else if (keyboard_check(vk_up)) {    Direction = "Up";    sprite_index = CaseyUp;}else if (keyboard_check(vk_left)) {    Direction = "Left";    sprite_index = CaseyLeft;}if not (keyboard_check(vk_down)) { if (Direction == "Down") {sprite_index = CaseyDown;    }}

i tried changing up the code and what its supposed to do is to play the walking animation then repeat until key not pressed then set the animation to stop