The breast collar is hanging a bit low, to remedy this you can, make what is called a wither strap tie a piece of leather or para-cord from rings that the tugs are on over to the other side and tie it. The breast collar ought to sit over the shoulder so as not to impede movement of the shoulder.
As far as the tie down, it does not go on the breast collar. When used properly the tie down attaches to the girth, with a snap, goes through the d-ring on the chest plate and attaches to a nose-band. If the snap will not fit through the d-ring then you can tie a piece of leather or para-cord to the ring and run the tie-down through that. That said why are you using a tie-down?