If i remember correctly, the largest Blue-Ray disc is 128GB.
So Forza 8 would still be two discs!
I guess
Disc 1: 97.6 GB (Play disc)
Disc 2: 34.5 GB (Map pacs to be installed)
Reminds me of GTA V on the x360.
Chuck it on eBay or take it to CEX and get store credit.
Any kind of refund would be delt with at the point of sale and its them you would have to contact.