I don't know if you are travelling Sunday or Monday.
QR operates 2 flights in the evening (last morning flight departs at 9:05) and QR835 is the first evening one. I doubt that you can check-in over 3 hours before.

If you depart on Monday (national Holiday), it is not unusual that OLCI not open exactly 48h before departure. It might open a couple of hours later.

I doubt that any longhaul airline proceeds OPUP to F on a first come basis. In your case, all QR flights BKK-DOH are zeroed out on Sunday and Monday.
If you cannot even get a "confirmation pass" shortly before your flight, I would also be worried about a potential downgrade.
Opups and downgrades will depend on many factors such as your booking class (are you on a BA award?), status, etc..