Relax - and have an amazing flight!
You were able to allocate your seats as you are in First. Most Economy passengers on Garuda *cannot* pre-book their seats (I think fully flex Y & B Class pax only).
The flight is packed, only a few Business Class Seats left it will probably run at 100%. I flew Business on this route, and it was fabulous, so your F experience will be even more wonderful. Enjoy it!