carsauto,
Your car is done correctly. The floor panel had to be riveted to the body panel at that location because that section of the body is aluminum. The rest of the points to which the boot floor abuts are steel, and could be welded. The rivets should be flat head solid aluminum ones.
Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon