set block under raycast to red glass and back

ive got a boss datapack im working on and one of its attacks is a spinning raycast. i want the blocks under it to be set to stained red glass and then back to grass, sort of like the red glass is following it. this is inside the raycast code
fill ^-3 ^-1 ^ ^ ^-1 ^ grass_block
setblock ~ ~-1 ~ red_stained_glass 

somehow, this doesnt work. it just sets the glass to grass