AFAIK the right is 0 degrees, and the angle everything faces by default.
Look at a sprite and you should see a small arm coming off the center of it, moving that will change the angle within the layout and should change the default angle for that particular sprite then.
The bullet behavior I think is made to go in the direction the spawning object is facing. But I doubt it would be that difficult to make it choose a random direction either.
Since this is the grapple, right? Are you sure using the bullet behavior is a good choice? While more in depth, you might find you get more control by setting up it's behavior through events alone, and just use the bullet behavior for bullet like objects. (I know, I know, depending on deployment, a grapple could be considered a projectile). But for your purposes maybe something else would work better.
Personally I'm tempted to suggest using physics for it.