Get some better epoxy, i fix little crap like that all the time with good epoxy no problem.. Get this stuff called plastic welder epoxy, some auto parts stores carry it and its like $7 a tube. You squeeze it out and mix the two parts together and apply.
Take some light grit sandpaper and rough up the mating surfaces, then make sure the two parts are CLEAN. Hot soap and water and some alcohol. Make sure the parts are room temp also that helps it cure faster.
Apply a good amount of epoxy to the back of the panel and then press that piece into the goop and work it around, you have some time to work with it until it sets up, make it look like a nice weld all the way around the piece. Once it sets up enough that it will sit on its own, usually ten minutes or less, then just let the sucker cure overnight. You will actually feel the plastic get warm around the area thats being glued, and i have accidently distorted thin plastic with it before.
If you do it right its stronger than the original surrounding plastic. The only time i ever had a piece re-break that i fixed it actually broke in a new spot, the epox itself didnt crack or break.
