Hey @sungmin_0203! Welcome to the forums!
So there are a few things to consider!
If the projectile movement component on the projectile actor is set to a NEGATIVE value, it will go backwards. A straight forward moving projectile should have a positive X, 0 Y, 0 Z on the movement values.
If the spawn point’s forward (the RED arrow on the movement widget) is not in the direction you want, it won’t go that way.
If the spawn code has an incorrect position, it could fire the incorrect direction.
Check those things and then if that doesn’t work try to get us some visuals of your code! 