Hi Lou, my tonneau came with 16 Tenax and I'm not going to guess where your rings fit. The two corner studs inside the windscreen are difficult to use so that's a possibility (and I hadn't noticed before that they and the other dashtop ones were smaller). Ask your supplier and, perhaps, ask for two Tenax instead of the rings.
Unless you want to cut the holes with small scissors you will need a 3/8" (10mm) hole punch like the one here:
I made the little centre finder with a bit of wooden dowel, which would slide up the punch, and stuck a small nail up a hole in the centre of it.
Engage the tonneau cover in the slots on the rear deck, fit the wheel pocket over the wheel and pull the cover gently into its working position. Pulling it out gently all the time, press it down on each fixing stud in turn and mark the point's position with a felt tip pen or ball point. Then move to a workbench and align the punch on each mark, with a device like mine or marking a circle, and hit it with a hammer. Use a bit of scrap wood behind the tonneau material to save your work surface. If using scissors mark a circle to cut to. Either way just screw the Tenax together and fit.