Scott hadn't even noticed that Derek was in the woods that night at as well but he was thankful for the help, especially since he knew Stiles was so worried that he was going to get eaten now. How were they all going to get out of here alive? Erin was strong and powerful, powerful enough to take them all on if she really wanted to.
"Derek! No! It's not safe." he yelled trying to get Derek away from Erin, but maybe he should've just kept on running. He saw Stiles there and was glad that he made it out of Erin's way. He grabbed Stiles by the arm so they both could leave the woods together and get out of there safely. He should've stayed and helped Derek though.. he probably should just go back.