Pants-wettingly terrified would be a good way to describe Selwyn's state of mind right now. He'd put his name in that cup thinking he had as much chance of being chosen for this dubious honour as he did of sighting a crumple horned snorcack in the Slytherin Common Room before breakfast next Tuesday.
When Shacklebolt called all of them to the antechamber, though, all the excitement Selwyn had been running on after the announcement of the champions had evaporated as it was suddenly brought home to him that this was real and there was a chance that he would, if not die, then at least be seriously injured some time during this year.
Nevertheless, Selwyn Thorfin was also a Slytherin. He wasn't out and out evil, and he may not have wanted to take over the world, but he knew how to spin a situation to his advantage. He'd lingered long enough for people at other tables to be looking at him, now. Long enough, in fact, for his own house-mates to be asking if anything was the matter. Selwyn shook his head as though shaking away a cloud of unpleasant thoughts, took a deep breath and went to join the others in the antechamber.
"Well, I suppose now's the time to wish each other good luck," he offered a hand to his competitors.