The England Under-21 international netted 20 times for the Baggies last term.
“I make mistakes,” he added. “I hold my hands up and I say it was a mistake from me. I just apologise to all the fans out there that have always supported me and also the club that has always believed in me.
“I have missed a lot of football and I am just trying to get myself back into match fitness and sharper again like I was last season.
“My focus is mainly on getting back to what I was last season and finishing really on a high.”
West Brom are 14th in the Premier League and entertain Crystal Palace on Saturday.