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