Welcome to AF bsg01 !
Hav you tried jiggling the key around to see if it will come unstuck ?
If not the lock cylinder is the problem and needs replaced. Here is a link for the R&R on this part.
Ignition switch-Lock Cylinder check/replace 99+ Grand am's
Also if the break shift interupt is bad, or a blown fuse, it can keep the key stuck in the "on" or "run" position.
Hope that helps.