No, that's not the right part.
The missing fitting is made of bright yellow plastic with a circular head that slides into the moulding you have highlighted. The other end of this fixing sticks out and locates in the corresponding socket in the main N/S rear interior trim. TBH it's a real PITA as every time you go to fit the tool storage cover it falls out. It's a stupid piece of design. I've always meant to glue mine in place to stop it moving but haven't got around to doing yet.
Have a root about in the tool compartment as it's probably fallen off and is inside there.
If you want a photo of the missing part let me know and I will sort it out tomorrow. The boot is rammed at present and it's probably raining as usual.