Boot lining sagging

[Duff3103]

So ever since Iv had my w211 my boot lining has always sagged into the spare wheel well with weight on it and to be honest it’s really doing my nut in now so clearly I must be missing something wether it be a trim or some sort of support to hold it flat and flush

Can anyone elaborate what I may be missing? I have a spare wheel all be it a space saver, some plastic trim for the middle but I’m not sure if this is all there should be

Thanks in advance