The finishing when he hit the post was actually pretty solid. With an Osasuna player tugging his shirt and facing away from the goal that was far from an easy finish. A couple of inches to the left and that would've been a goal.
He has amazing physique and he can read the play quite well but his inexperience shows in games like this. Sure, Arda's foul was stupid but Varane did the exact same thing and then let Suarez score.