give your player bullet behavior.set it disabled on start
when enemy on collision with player
player x<enemy x then
set player platform behavior disabled
set player bullet enabled
set bullet angle of motion 180
wait x seconds (you decide)
set player platform behavior enabled
set player bullet disabled
when enemy on collision with player
player x>enemy x then
set player platform behavior disabled
set player bullet enabled
set bullet angle of motion 0
wait x seconds (you decide)
set player platform behavior enabled
set player bullet disabled
this way you can set any speed for the bullet until you are happy with the result
tip if you want arched hitback then set gravity for bullet to on and go for bullet angle of motion to 240 and 320 !