2001 Pontiac Grand Prix ignition problem

So today I went to work and when I got there I turned my car off, and found I couldnt completely turn the car off its stuck in the last position b4, the car is off. But u can remove the key. And I then turned the ignition and the car started up, with no key in the slot, im afraid if I leave the car outside in the area I work in someone will find out they can do it and steal the car:( so any info will be greatful, I think I should replace the ignition and steering colum all together($) but if I can save money someway ill do that

thanks
justin