Don't force it! Things will break and you will regret it.
I had a tape stick in mine once. It's not too hard to fix it, you just need a little patience.
The best way to get the tape out is to remove the stereo from the car and take it apart. It is not as scary as it sounds - these units were built for servicing. Gently remove the plastic bezel from around the stereo and heater controls. It is held in place by clips (careful, theytend to fly off and are easy to lose). Next, unbolt the stereo from the dash (there are four bolts holding it in place). Now slide the stereo out and unplug the wires from the back, including the antenna wire.
If memory serves me correctly, you remove the bottom plate off the stereo, then unscrew and remove the tape drive unit from the rest of the stereo. It is a modular design, so it comes out easy - just keep track of the screws you are taking out so you can reverse the process.
Now it is just a case of playing with the motor drives for the tape mechanisms by turning them manually until the tape is ejected. A little bit of patience and trial and error and the tape should come out ok.
I know it sounds like a lot, but it only took me about half an hour to take the stereo apart, figure out how to get the tape out, and put everything back together, and I'm not the sharpest tack in the box, mechanically.