If you are already down to the tree line and you have frostbite, I would say keep going to keep warmer..
That aside..
I would find a large rock/stone and some ideally spaced trees. I would thread the tarp all around, and the loops of cord from the eyelets going enough times around a tree to hold it, and then pass the cord through the next eyelet, and so on until you are back to the first eyelet. Pass the cord through it and then wrap both the ends of the cord around the rock enough times to hold it.. If the rock/stone is not quite big enough to hold the tension, I would push a stick into the ground (between the cords) to hold the rock back..
Does that make sense..? I could explain it better with a drawing..