Since fitting fmic bumper has not fit 100%. The very last tab does not click in on either side. Anyone have any ideas? I've put the 3 plastic rivets back in.

Is the bumper the correct side of the plastic tab? you have to kind of bend the bumper around it.

If so then you could need new side clips. Quite cheap from skoda

Pretty sure you will have the bumper on the wrong side of the bracket at the rear,where the screw goes through from under wheel arch area.