"She told me to call." The thought of seeing Wanda again, now that Loki had revealed her for her true intentions, made Billy's skin crawl. But... this was a chance to prove himself, beyond simple tricks and trainings. This was real.
"I understand it's dangerous... but I can do this." He had to prove it, not only to Loki, but to himself, that he had what it took to deal with magic. Not only the actual magic itself, but also the ups and downs, friends and foes that came along with it.