"I've got a year left on my contract now," Turnbull told the Evening Gazette.
"I'm definitely playing for my future and there's nothing more that I want than to stay and be the No.1 goalkeeper, and with a year left it's down to me to show them what I can do.
"People say I haven't got experience but I've been out on loan and played games in the lower divisions. That's how you get experience.
"I'm definitely ready for it. I've never been more focused and fitter.
"I feel really good at the moment so I need to maintain that and see what happens on August 16."