The Gunners must now win against Olympiakos in Athens to stand any chance of finishing top and so head into the last 16 as one of the seeds.
Wilshere knows they have to get better and told Sky Sports: "We started off sloppy. But we've still got one game left. We need to finish top.
'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 added: "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."
Wilshere ran to embrace the Arsenal physio after scoring and of his own recovery, he said: "It (fitness) will come - I've never been injured before so I can't tell you how long it will take."