Miyaichi acknowledges that he failed to take his chance in what was only his fifth appearance of the season.
"Obviously we were disappointed, for me as an individual as well," he told the club's official website.
"I would say [my performance] was not good enough. I'm not satisfied on my individual things but we have a lot of games to go so I want to prepare for that. Let's focus on Liverpool on Saturday."
Arsenal play host to Liverpool in the Premier League this weekend.