I have never yet ordered a piece of harness or tack equipment that didnt' need tweaking. Even a harness I sent measurements for needed tweaking. So, it's pretty normal to have to make things work for a particular horse.
I just got a mini pack saddle in the mail yesterday. It is nylon, so I've been busy melting new holes, trimming, restitching--getting it to fit my horses. But it will be fun to play with and worth it.
btw, ddidn't you just love getting the pile of leather straps in a box and trying to sort them out!