Within the ProjectileMovementComponent settings, set gravity scale to 0. That will make sure your projectiles move in a straight line and is not affected by gravity.
To shoot exactly at the cross hair, however is a little bit more involved. The trick is to find a vector towards the world position of the cross-hair and set this as the rotation for your projectile. You can use Converted Screen space to world space node to get the world position of the cross-hair.