A couple of things to try:
- shut the car off; normally, if in a F/R gear, it will then automatically shift into P
- with your seatbelt off, open the driver's door - this normally also puts it into park (doesn't do it if your seatbelt is on, though).
- make sure the button is not stuck down
- make sure that there is the normal spring tension on the shift knob and that the thing isn't stuck or misaligned (excessive force used to shift it?).
- see if you can slightly move the shift lever a bit one way or the other and while moved, see if it will go into park.
Scan through the user's manual and see if you can figure out which fuse controls the transmission, then momentarily pull it and reinsert. See if that does anything.
There's a mode you can put the car into while going through a car wash that prevents it from going into park so it can be pulled through via the mechanism...maybe that sequence was activated. Check the manual on how to reset it. Similar thing in case you need to pull it or push it somewhere, you can lock it into neutral so, say, it could be pulled up onto a tow truck flatbed.