Unfortunately, the fiberglass part has probably been epoxied to the steel. It's a common manufacturing technique in the industry to bind two disparate materials together. Screws would require a number of structurally weak points whereas epoxy can cover most of the two surfaces without compromising material strength.
You will probably have to resort to a full trunk lid replacement.
Rook
You will probably have to resort to a full trunk lid replacement.
Rook