The Gunners booked their place in the last 16 with a 2-0 victory over Montpellier at the Emirates, Wilshere and Lukas Podolski both scoring fine goals in the second half.
It was Wilshere's first goal since his comeback from injury and although he was delighted Arsenal have confirmed a place in the last 16 for the thirteenth consecutive year, the midfielder says they have plenty of work to do.
"The first half was hard - we were sloppy, we gave ball away and weren't ourselves so needed to come and get an early goal," he told Sky Sports.
"We have to step it up. Tonight wasn't good enough, especially in the first half.
"We've got to play the best teams to win it so it doesn't matter who we get (in the last 16)."
Podolski's goal was stunning - a one-two with Olivier Giroud followed by a first-time volley on the run which arrowed over the keeper and in.
"It was a great goal, it's little bit lucky when you score like that," said the German. "We are happy with three points and we're looking forward to playing Olympiakos.
"We must keep fighting - we have a tough game at Olympiakos and we want to finish top of the group."