David, I know what happened. You need to slide in the bumper EVENLY and make sure both sides snap in. Sometimes I had the bumper in but one side wouldn't snap(no matter how hard I push). Do this and the bumper should be secure.
*As for removing the rear bumper, it's quite easy.
you have to remove the plastic piece the covers the lip o the trunk after that you remove 1 nut (middle of drunk mat and lip) then there are 2 nuts that need to be removed on the right side as well as another 2 on the left. then just slide the bumper off. hope it helps
Hristo, there are no sensors and the gap is normal.