How are you finding the Alpkit pd800 I’ve still not decided on one of these or the 600 ??
Also looking at your kit list I think you will be fine.
What do you wear in your bag ( any extra clothes )
If you can make yourself a little fire it’s great for heat and cheering you up when it’s cold.
Also as flatfish says try a couple of the hand warmers thrown in your bag before you jump in.
See if you can get some natural insulation under your bivi as well ….if your in the forest get some evergreen pine branches to make a kind of mattress……….that will take the edge off.