I'm confused, did you try to glue a screen to a hole in your dash using bondo? Because thats not really how fiberglassing works.
Make a mount that mounts to the existing cd player mount in your car and get the screen working. Then get a dash trim cover, cut a hole, use bondo to make it look pretty, then install on your car.
A body shop could probably do this for you, possibly a stereo install shop too.