It is windy out there right now. If you can block the wind that will be the most help. Pull your tarp way down and maybe even pile a little snow to make a low wall on the windward side of the tarp.
Wear an extra layer of insulation (light coat or long underwear), you can always take a layer off if you are too warm; eat a hearty meal before you go to bed and don't forget a bit of chocolat to snack on should you wake up. It will give you that extra energy boost to keep you warm about 3 am.
If thing aren't working out don't be afraid to go inside. It is better to get a good nights sleep and think about what worked and what didn't in the morning (been there - done that).
Oh yea wave at all your neighbors who will be looking out their windows at you wondering what the ****is going on.
(been there - done that)