There is a choice of two fitting kits , depending on whether you have a saloon/coupe with the wheel lying horizontal under the floor , or an estate with the wheel mounted vertically at the side .
Your dealer should have offered you the choice when you purchased the can .
The kit for the estate car comprises an extension bolt which replaces the original angled wheel retaining bolt - the 'new' one has the same male thread at one end , then opens out to a flange at the other end with two 'wings' for tightening to retain the spare wheel and a female thread in the centre to accept the bolt for retaining the can .
If you go back to your dealer , with the part number for the can , your dealer shpuld be able to look up the fitting kits . When I bought mine , about 15 or 20 years ago , the can was about £40 and the fitting kit was something like £5 or £10 from memory .
If you don't get anywhere with the dealer , I'll photograph mine and post a picture here .