It's possible to have a reservation in a cabin you're not ticketed for.
Airlines will hold a reservation for a specific amount of time in order for tickets to be issued. Periodically, they'll validate that a reservation has a ticket associated with it, and whether that ticket is valid. If it isn't, they could cancel the reservation. (e.g. Redemption bookings on SQ must be ticketed within 24 hours or the reservation is cancelled // I once reserved a seat on OS VIE-SYD in March but didn't ticket it until September).
The crunch time is when you have the boarding pass issued - this converts your reservation and the associated ticket (segment) into a specific seat. If the system is working right, the ticket must be validated for the flight/cabin you're being seated in.
I can tell you from personal experience that using an eGUV requires the ticket to be reissued and revalidated. I used an eGUV to upgrade myself and a colleague on LHR-DME, and my reservation showed 'Confirmed' in the business cabin. However, when I got the LHR, I could't check in because the tickets hadn't been re-issued. I had to go to the ticket counter, where they re-issued/re-validated the ticket for me. Then I could go and check in and get a boarding pass.
Don't panic at this stage - there are sometimes disparities between airline ticket rules, reservations and associations between fare buckets and cabin classes. (For instance, flying a Business ticket on sectors that only have Economy seating). As long as you've paid for, and been issued, a ticket in a 'Business' fare bucket, it should sort itself out, or it'll get sorted out at check-in.