Gadzooks. It looks big big. When I ordered my Liberty harness from Amber a Hillside/Ron's, I got an email confirming size measurements. So wow, if Mitch of the honking huge cranium and schnoz can fit their cob bridle, holy moly, that bridle you got is a whopper.
Just checking because I can't tell from the picture, but you did loop the end strap where the bit goes back through the noseband right? The way my bridle from that company came, it had the strap going down, the bit fit on the end loop and then the strap went back up through the slot on the noseband and buckled to the buckle. Not that it really might make a difference for you if you tried that, but it would mean you could move the noseband down towards the bit and maybe take the buckle up more hole (although it's on the last setting, right? Might mean it's too big period.
You might try asking for a trade on Carriage Driving Classifieds on Facebook. Or one of the other harness groups. I know a couple. I'll check my tack, I think I have a bridle left from my first harness, but I can't verify that until the morning.