Help with fitting a part

The previous owner had fitted a roof rack to my 1.4 elegance hatchback but removed it on selling it leaving eight holes in the roof trim. I ordered the small black plastic tabs from my skoda dealer, but I cant fit them they dont just clip in they have two small tabs on each side so you cant just clip them in. The trim itself looks like it has a channel in it so I removed the strip from the car and placed the tabs in from the under side using some clear tape across the hole from the top side to hold them in place. I put the strip back on the car all lined up right but when I take the tape off they just drop on one side into the hole almost as if they dont fit. Please help has anyone had to do this Im thinking of using a glue to hold them in place its driving me mad. many thanks all.