I took it back where I bought it from and they showed me that one is pretty the size they carry (mine was even a little bigger then some) they suggested rigging up an extension even a small nylon dog collar on each side for length.
Thats kinda what I am wondering. Do you ride western or english and what breed is your horse? Most tack comes in standard sizes that should fit the average size horse 800lbs to 1200 lbs. They will fit bigger if you punch more holes and will also fit smaller with more holes.