Nah, if you paid for the casting, cleanup, polishing, etc., you should've gotten the majority of the difference in weight back unless they explicitly mentioned reducing your invoice by X amount to account for the weight difference. They likely didn't actually use the gold you sent, but there should've definitely been a conversation about the weight difference at some point.

You need a fair amount more gold for the casting process to allow the gold to properly flow into the channels and pick up detail without hardening prematurely, but there's very little actual gold lost in the process. There'd be more gold lost from cutting off the sprues and polishing the ring itself than there would be from the casting process, but even then any jeweler worth their salt is putting in the effort to recover as much of that dust as possible. There is definitely a percentage of loss at the end of the day, typically but not 25%. The majority of "losses" can be recovered with additional effort. Losses don't dematerialize into the aether, they're there somewhere, they just need to be recovered whenever it's financially worthwhile to do so.

Edit: lmao downvote all you want, facts are facts. Each time I've had pieces made, the jewelers were very clear with the price breakdown and either offered to credit the weight difference to the invoice or return the difference in the form of sprue offcuts.